2.1.0: new report to allow val3dity to support more data models

The core validation stayed exactly the same, no changes. Only these were modified:

• the report is slightly changed: the CityObjects/Primitives subdivision in the report is replaced by Features having Primitives, where Features are the top-level objects, containing one or many Primitives. This is done to allow other data model to be used as input, eg IndoorGML is coming soon!
• pytest allows to specify the binary to use if not under 'build/'