New windowing system

Large commit that totally refactor of the way we handle the bar and
panels.

Testing should focus on Panels, Bar, Keyboard Focus, IPC calls.

Changes brief:
- One NFullScreenWindow per screen which handle it's bar and dedicated
panels.
- Added shadows
- Reintroduced dimming
- New panels animations
- Proper Z ordering
- Panels on overlay laywer is not reimplemented, if we do it then the
bar will be on the Overlay too
- Panel dragging was not reimplemented, to be discussed before
reimplementing
- Still a WIP, need to work more on shadows and polishing + debugging.

Modules/Settings/Tabs/UserInterfaceTab.qml

@@ -26,6 +26,13 @@ ColumnLayout {
       onToggled: checked => Settings.data.ui.tooltipsEnabled = checked
     }
 
+    NToggle {
+      label: I18n.tr("settings.user-interface.dim-desktop.label")
+      description: I18n.tr("settings.user-interface.dim-desktop.description")
+      checked: Settings.data.general.dimDesktop
+      onToggled: checked => Settings.data.general.dimDesktop = checked
+    }
+
     NToggle {
       label: I18n.tr("settings.user-interface.panels-attached-to-bar.label")
       description: I18n.tr("settings.user-interface.panels-attached-to-bar.description")