Major modmgr overhaul
Add missing formspec checkbox doc

This reverts commit 7dbbbfc6.
(was added twice)

Show server description above connect button instead of in favorites list

Add alphabeticaly sorted worldlists
Select world after creation
Move worldlist handling to separate file
Merge world selection of singleplayer/server tab
Remove some useless code

This reverts commit 39d03148.

Always use address for server
Fix first (empty) element beeing selected after deleting last world

make enter button work in create world dialog