Bugfix: selecting shapes wouldn't enable KoFillConfigWidget

This signal was wrongly removed (in fc362afc) under the assumption it is an alias to selectionContentChanged() signal.

This signal doesn't need blockers, like it did previously, because the blockers were meant to stop the selectionContentChanged (e.g we change the color and it would fire selectionContentChanged(), to which we'd respond with again updating color -- a cycle).

Test Plan

To test this one has to extensively test the Vector Shapes, KoStrokeConfigWidget and KoFillConfigWidget. By creating shapes, selecting, changing the fill of the shape, color, testing the widget by switching between fill types.