add library interface class and make library frontend exchangeable
remove obsolete generator class
fix: correct output for unit conversion
fix: remove generator from SWIG input file
cosmetics doxygen
introduced 'library_handle' to forwards
fix: proper handling of python module imports
extend examples for python module import
Merge branch 'python_backend' into next
Merge branch 'python_backend_fix' into next
Merge branch 'next' into ipd2xml

Conflicts:
	src/library.cpp