QML: add navigation items

- Add a NavButton, which shows a directional arrow, and fades in on hover.
   It can be used left- or right- by setting an image source
   and click handler.
 - Specialize NavButton to Forward and BackButton.
 - Add a SlideCounter navigation aid.

src/qml/calamares/slideshow/BackButton.qml

@@ -0,0 +1,24 @@
+/* === This file is part of Calamares - <https://github.com/calamares> ===
+ *
+ *   Copyright 2018, Adriaan de Groot <groot@kde.org>
+ *
+ *   Calamares is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   Calamares is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+NavButton {
+    id: backButton
+    anchors.left: parent.left
+    visible: parent.currentSlide > 0
+    isForward: false
+}

src/qml/calamares/slideshow/ForwardButton.qml

@@ -0,0 +1,23 @@
+/* === This file is part of Calamares - <https://github.com/calamares> ===
+ *
+ *   Copyright 2018, Adriaan de Groot <groot@kde.org>
+ *
+ *   Calamares is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   Calamares is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+NavButton {
+    id: forwardButton
+    anchors.right: parent.right
+    visible: parent.currentSlide + 1 < parent.slides.length;
+}

src/qml/calamares/slideshow/NavButton.qml

@@ -0,0 +1,68 @@
+/* === This file is part of Calamares - <https://github.com/calamares> ===
+ *
+ *   Copyright 2018, Adriaan de Groot <groot@kde.org>
+ *
+ *   Calamares is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   Calamares is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/* This is a navigation (arrow) button that fades in on hover, and
+ * which calls forward / backward navigation on the presentation it
+ * is in. It should be a child item of the presentation (not of a
+ * single slide). Use the ForwardButton or BackButton for a pre-
+ * configured instance that interacts with the presentation.
+ */
+
+import QtQuick 2.2;
+
+Image {
+    id: fade
+    
+    property bool isForward : true
+    
+    width: 100
+    height: 100
+    anchors.verticalCenter: parent.verticalCenter
+    opacity: 0.3
+    
+    OpacityAnimator {
+        id: fadeIn
+        target: fade
+        from: fade.opacity
+        to: 1.0
+        duration: 500
+        running: false
+    }
+    
+    OpacityAnimator {
+        id: fadeOut
+        target: fade
+        from: fade.opacity
+        to: 0.3
+        duration: 250
+        running: false
+    }
+    
+    MouseArea {
+        anchors.fill: parent
+        hoverEnabled: true
+        onEntered: { fadeOut.running = false; fadeIn.running = true }
+        onExited: { fadeIn.running = false ; fadeOut.running = true }
+        onClicked: {
+            if (isForward)
+                fade.parent.goToNextSlide()
+            else
+                fade.parent.goToPreviousSlide()
+        }
+    }
+}

src/qml/calamares/slideshow/SlideCounter.qml

@@ -0,0 +1,37 @@
+/* === This file is part of Calamares - <https://github.com/calamares> ===
+ *
+ *   Copyright 2018, Adriaan de Groot <groot@kde.org>
+ *
+ *   Calamares is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   Calamares is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/* This control just shows a (non-translated) count of the slides
+ * in the slideshow in the format "n / total".
+ */
+
+import QtQuick 2.2;
+
+Rectangle {
+    id: slideCounter
+    anchors.right: parent.right
+    anchors.bottom: parent.bottom
+    width: 100
+    height: 50
+
+    Text {
+        id: slideCounterText
+        anchors.centerIn: parent
+        text: ( parent.parent.currentSlide + 1 ) + " / " + parent.parent.slides.length
+    }
+}

src/qml/calamares/slideshow/qmldir

@@ -1,4 +1,10 @@
 module calamares.slideshow
+
 Presentation 1.0 Presentation.qml
 Slide 1.0 Slide.qml
 
+NavButton 1.0 NavButton.qml
+ForwardButton 1.0 ForwardButton.qml
+BackButton 1.0 BackButton.qml
+
+SlideCounter 1.0 SlideCounter.qml