Improved module handling

This contains a few different things which improve module handling for me. With the keybindings, I tried to stay close to conventions of other programs, take a look whether you would change anything.

The module list is more convenient this way, but it's kind of unobvious how to close it again (using the "+" button). Any ideas?

Ah, and the keybindings aren't documented in the manual yet. Maybe it's more efficient to update (some kind of) documentation later, before a new release, instead of trying to keep it up to date while implementing stuff?