CHANGE FEATURE: include more possibilities to select the projections

Summary

The pushbutton to select the projection should be replaced or extended by a better control.

Reason

The button is rather uncomfortable and slow, and it limits the available projections.

Detailed explanation

The basemap is handled via the projection formatoption that can have strings or cartopy projections. Now idea what the best solution is here to include it in the GUI. Any idea @tobstac?