All CityObjects are now saved to a single
"features" table instead of per file tables.

Invalidates all Cache entries before starting parsing of a new file to
prevent cached CityObjects being unintentionally transferred to wrong
database table.

BREAKING CHANGE: Implements the saving and loading of CityObjects to a
GeoDB with in-memory caching. This allows reading of bigger CityGml
files and serves as basis for the implementation of Topological Checks.

CityDoctorModel will now return Streams instead of Lists for the
CityObject-getters (like getBuildings()). This requires a rework of all
methods calling them.

# Conflicts:
#	CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/datastructure/GenericAttribute.java