Made the chatroom list persistent.

IMHO it's annoying at best to have to re-open all chatrooms you had open the last time every time you start the program, so... here's the fix.

Also did some code cleanup and minor refactoring while I was at it... what a mess o.O
And I fixed one german translation error (neither genitive nor plural require an apostrophe in german... much less a backtick (`)).