Add string constants for building names

[mayant15]

Create a new BuildingNames class with string constants to be used everywhere in the module. Will facilitate easy renaming of buildings.

Originally suggested for Terasology/MetalRenegades#27

[skaldarnar]

Hm, many buildings come from other modules, and are not part of DynamicCities itself. How would that be supported by String constants in this module?

Maybe this needs some more thought before it becomes actionable. @msteiger anything to add from your side?