#17 snapping button is on start not selected
#17 on add new Polygon ore new Point, Snapping Button is also set to selected
#17 on click on snapping button, also enable Snapping in ReadOnlyMode
#17 snapping is only activated/deactived with a click on the snapping button. Furthermore it is actived when a new Point or a new Polygon is added.
Merge branch 'bug/17-snapping-mode-is-off-but-Snapping-Button-is-selected' into feature/11-undo-buttons-for-tables