Embedded GeoDB implementation

Summary

Rework CityDoctor's internal model by implementing an embedded GeoDB.

Implement an embedded GeoDB and serialization to/from CityDoctor's internal model.

Usage of a GeoDB offers many benefits:

Allows hardware paging via serialization, reducing memory usage and enabling the implementation of a memory cache
Enables usage of spatial functions like intersects, buffers or contains.
Enables tiling of big CityGml files, removing memory limitations of CityDoctorGUI
Necessary for the implementation of topology checks
Native implementations of BBox and spatial index simplify selection of neighbouring CityObjects
Simplifies combining different files (e.g. CityModel, DTM and PointClouds).