[libcalamaresui] Stub requirements checking.

Introduce a method checkRequirements() into the module system so that
individual modules can do their own checking (as opposed to stuffing
it all into the welcome module).

src/calamares/CalamaresApplication.cpp

@@ -355,6 +355,7 @@ void
 CalamaresApplication::initViewSteps()
 {
     cDebug() << "STARTUP: loadModules for all modules done";
+    m_moduleManager->checkRequirements();
     m_mainwindow->show();
     ProgressTreeModel* m = new ProgressTreeModel( nullptr );
     ProgressTreeView::instance()->setModel( m );

src/libcalamaresui/modulesystem/Module.cpp

@@ -297,4 +297,9 @@ Module::initFrom( const QVariantMap& moduleDescriptor )
     m_name = moduleDescriptor.value( "name" ).toString();
 }
 
+void
+Module::checkRequirements()
+{
+}
+
 } //ns

src/libcalamaresui/modulesystem/Module.h

@@ -1,6 +1,7 @@
 /* === This file is part of Calamares - <http://github.com/calamares> ===
  *
  *   Copyright 2014-2015, Teo Mrnjavac <teo@kde.org>
+ *   Copyright 2017, 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
@@ -161,6 +162,11 @@ public:
      */
     QVariantMap configurationMap();
 
+    /**
+     * @brief Check the requirements of this module.
+     */
+    virtual void checkRequirements();
+
 protected:
     explicit Module();
     virtual void initFrom( const QVariantMap& moduleDescriptor );

src/libcalamaresui/modulesystem/ModuleManager.cpp

@@ -315,4 +315,18 @@ ModuleManager::loadModules()
     } );
 }
 
+void
+ModuleManager::checkRequirements()
+{
+    QTimer::singleShot( 0, this, [ this ]()
+    {
+        for (const auto& module : m_loadedModulesByInstanceKey )
+        {
+            module->checkRequirements();
+        }
+
+        emit modulesChecked();
+    } );
+}
+
 }  // namespace

src/libcalamaresui/modulesystem/ModuleManager.h

@@ -80,9 +80,16 @@ public:
      */
     void loadModules();
 
+    /**
+     * @brief Starts asynchronous requirements checking for each module.
+     * When this is done, the signal modulesChecked is emitted.
+     */
+    void checkRequirements();
+
 signals:
     void initDone();
     void modulesLoaded();
+    void modulesChecked();
 
 private slots:
     void doInit();