Released version 2.1.0

This release has minor bugfixes and major feature enhancements.

You now can specify radio buttons and button groups in the dialog feature for buttons (see documentation). The whole mouse-grabbing was reworked and works now as expected. Also the session management should now not detect the loaded XApplications inside the buttonbar.

The icons now can be hidden and only the text displayed and subbuttonbars will open now on drag-enter events.