QmlDesigner.PropertyEditor: Adding dirty flag to LineEdit

This patch ensures that we only commit data to the backend
if the text actually changed. The signal onEditingFinished is triggered
even if the user did not edit the string.

Change-Id: I2d54f3d79a1c60525e4c9744b364cc014bd407ce
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
QmlDesigner.PropertyEditor: Use selectionToBeChanged in LineEdit

Commit any data to the backend if the selection will change.
The signal editingFinished is usually triggered to late.

Change-Id: Ib7adfd32a50ae94b017a7587e81721176440a988
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
QmlDesigner.PropertyEditor: Adding signal selectionToBeChanged

Controls can connect to this signal and commit data to the backend
before the slection changes.
This is required since editingFinished signals are usually triggered to
"late".

Change-Id: I99fa27064473ceee2d1a21b25f64a13370fb4cef
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>