cleanup code

See merge request !24

Solid self intersection with better triangulation to eliminate false positives

See merge request !23

Synchronize Dev branch with Master

See merge request !12

(cherry picked from commit 2bf3cfb6)

(cherry picked from commit 8f9cd0d5)

CityDoctor Release Version 3.16.0

See merge request !11

CityGML 3.0. Support

See merge request !10

Hardcoded the CityGML version for parser tests with mock-files. The tests did still assume that the CityGML version is hardcoded in the writer, rather than being parsed from the input file.