removed "ChangeDataBase". see #106

removed the action from the "References" task for now until we have the
workspace's icon toolbar
after that we need to use WorkspaceController.getMapProject() for the
ribbon action and (like now) WorkspaceController.getSelectedProject()
for the icon toolbar
fixes the main part of #105

always opens the dialog where a user is allowed to either select an
existing project, create a new project or directly close the map
--> TODO; handle internal map open actions --> we can't directly close
maps, they might be needed internally
Merge remote-tracking branch 'origin/ribbons' into ribbons
fixes #105

refactored listeners code into new handler,