cache - WIP
Added mesh_cache models to 'admin' interface
Fixed creation of multiple layer entries in the database
Finished basic cache implementation. Request to MeshFactory is still missing.
Added conversion from GetTile parameters to GetScene parameters
Delegate requests for non-cached data to the MeshFactory
Fixed boundingBox parameter in GetScene request to MeshFactory
Added example implementation to MeshFactory to load a json-file as response to a GetScene request
Fix for wrong json decoding