Added test cases which test the public methods of the KNXCoreTypeMapper
class according KNX "System Specifications, Interworking, Datapoint
Types" Version 1.07.00.
Some tests revealed bugs in openhab and calimero. Theses tests testing
the wrong behaivour such that they don't fail.
Added a workaround for locale specific conversion of Float to String and
vice versa in Calimero.
Merge pull request #1254 from snow1111/KNX_datatype_enhacements

Added test cases for KNXCoreTypeMapper