Design mode/Qt Designer: Clean up the widget part of it.
- Remove shared subwindow reparenting from EditorWidget, make EditorWidget inherit FancyMainWindow. and use just once instance of it instead of per-editor ones. - Embedded FormEditorStack into EditorWidget as a centralwidget. - Changed FormWindowEditor's base class from IEditor to SharedTools::FormWindowHost (Widget) to be embedded into FormEditorStack (no need to be an IEditor), Remove Designer::Internal::FormWindowHost which had little functionality. - Add Design Mode widget to FormEditorW which has FakeToolBar and EditorWidget (single instance) in a vertical layout. - Removed ProxyAction class handling dock view toggle actions of several EditorWidgets (no longer necessary since there is just once instance). Moved "View menu" to bottom. - Started to make FakeToolBar work as a single instance listening on changing xml editors - Include-file/slot connection clean-up.