Fix for select descriptive file relations
Fixed creation of DS_ENUM attributes
Added custom serializers for datatypes Float/DoubleComplex
Fixed loading of multiple FILE_RELATION attributes in context
Added type spec BYTESTR_LEO

Change-Id: I7a32839312998232dc3bb4cd0a60ab7680e51974
Signed-off-by: Matthias Koller <m.koller@peak-solution.de>