Bugfix: Grid

The grid wasn't able to process areas with the size 1 properly.
added center option to labels
Bugfix: labels in windowed mode

Labels weren't displayed corretly in windowed mode
Added 2 new fonts for labels and buttons

Also, fonts can now easily be added and switched
Bugfix: grid/areas with width or height=1

The grid wasn't able to process areas with width=1 or height=1 properly.
Added skybox
Bugfix: buildings not correctly aligning to grid
Improved street building
Merge pull request #4 from ForceField-IndieGames/Benedikt

Skybox, better streetbuilding and various bugfixes [Benedikt]