PythonConverters: add ReadLonLat method
PythonGlue: split into separate source files
python: add Airspaces module skeleton
PythonConverters: add PyStringToString function

Used to convert a Python String/Unicode Object to a tstring. Unicode
objects are encoded as UTF8.
python/Airspaces: add addPolygon method
python/Airspaces: add optimise method
python/Airspaces: add findIntrusions method
python: replace NULL with nullptr