Tweaked camera zoom
Added placeholders to language files

Language files now support placeholders like %1%,%2%... which can be
used to fill in information.
Bugfix: City saved with wrong name (#35)

The cityname defined in the textfield was not used when saving the city.
Optimizations & Refactoring

Buildings can now have their own class. Also, buildings have click
events.
The size of save files was reduced by 50%.
Bugfix: Particles not rotating correctly

Particles did not rotate to the camera in certain angles.
Implemented citizens (#33)

Houses and big houses now slowly get inhabitants after they are built.
The citizens that lived in a house are removed when a house is deleted.
Merge pull request #37 from ForceField-IndieGames/Benedikt

Citizens, optimization, bugfixes