Enable changing defaultState of HistoryState in propertyeditor

Change-Id: I981857dd1cbb97c809ac879a1cfef45b023e1b0b
Reviewed-on: https://codereview.kdab.com/11335
Reviewed-by: Continuous Integration <build@kdab.com>
Reviewed-by: Volker Krause <volker@kdab.com>
Add missing UmlSimpleStateDelegate.qml to CMake QML_FILES

Change-Id: I308e421e320d2196bda62b4eb17b193f078e87f6
Reviewed-on: https://codereview.kdab.com/11399
Reviewed-by: Continuous Integration <build@kdab.com>
Reviewed-by: Volker Krause <volker@kdab.com>
Transitions are only allowed to be dropped onto states

Next steps:
* Fix dropping a transition onto state should set the
  state as source.
* Once a transition is dropped onto a state, a new drop
  should be initiated to define the target. That equals
  somewhat the UI-designer workflow to set connections
  between QWidgets.

Change-Id: I059b7517e30fad320241b5856142084e811855ae
Reviewed-on: https://codereview.kdab.com/11400
Reviewed-by: Continuous Integration <build@kdab.com>
Reviewed-by: Volker Krause <volker@kdab.com>
Made dropping transitions onto states proper work.

* Pass LayoutItem dragdrop-target to sendDragEnterEvent/sendDropEvent.
  This allows to attach a from the PaletteWidget dropped transitions
  direct to the drop-target.

* Attach from the PaletteWidget dropped transitions direct to the
  state they got dropped onto.

* Mark from the PaletteWidget dropped items the current one just
  like the user clicked on it after dropping.

Change-Id: I77790f046a05f4cd445d4b1666424baf38c76065
Reviewed-on: https://codereview.kdab.com/11403
Reviewed-by: Continuous Integration <build@kdab.com>
Reviewed-by: Volker Krause <volker@kdab.com>