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/Bar/Widgets/SessionMenu.qml

@@ -20,5 +20,5 @@ NIconButton {
   colorFg: Color.mError
   colorBorder: Color.transparent
   colorBorderHover: Color.transparent
-  onClicked: PanelService.getPanel("sessionMenuPanel")?.toggle()
+  onClicked: PanelService.getPanel("sessionMenuPanel", screen)?.toggle()
 }