Worldlist fixes
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
Add VoxelArea:position, VoxelArea:iter and VoxelArea:iterp
Disallow the name 'singleplayer' in a multiplayer server
Clean up bumpmap code a bit
Merge remote-tracking branch 'upstream/master' into masterserver