[usersq] Reflect editable in the QML

- if presets prevent a field from being editable, don't allow
  the user to edit the field
- while here, mention the changes in usersq

CHANGES

@@ -21,6 +21,8 @@ This release contains contributions from (alphabetically by first name):
    coded setup (which Calamares has had for a long time with @home
    and similar) and introduce a custom btrfs configuration through the
    `mount.conf` file.
+ - The *usersq* module now connects to the internal configuration
+   object and may be usable for regular installations.
 
 
 # 3.2.38.1 (2021-03-15) #

src/modules/usersq/usersq.qml

@@ -56,6 +56,7 @@ Kirigami.ScrollablePage {
 
                 id: _userNameField
                 width: parent.width
+                enabled: config.isEditable("fullName")
                 placeholderText: qsTr("Your Full Name")
                 text: config.fullName
                 onTextChanged: config.setFullName(text);
@@ -85,6 +86,7 @@ Kirigami.ScrollablePage {
 
                 id: _userLoginField
                 width: parent.width
+                enabled: config.isEditable("loginName")
                 placeholderText: qsTr("Login Name")
                 text: config.loginName
                 onTextChanged: config.setLoginName(text)