QmlDesigner: Add ContentNotEditableIndicator

If you hover over a tab the content will be visulized as non editable.

Change-Id: If7fcc8aaa319e0f952f501f6e9e2fc767b89b636
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
AmlDesigner: Refactor DesignerActionManagerView in a extra file

Change-Id: I50a74778f5fa0895110f2157728b9d99b677a6c5
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>