don't assign ID to Simple types

When adding entities, don't assign ID to Simple types.
Otherwise that type will be serialized incorrectly.

This fixes the issue with IFCPLANEANGLEMEASURE being serilzed
incorrectly when used as attribute to IFCMEASUREWITHUNIT.

With ID assigned, it will look like this:

  #10=IFCMEASUREWITHUNIT(#9=IFCPLANEANGLEMEASURE(0.017453293),#8);

The correct way to serialze is:

  #10=IFCMEASUREWITHUNIT(IFCPLANEANGLEMEASURE(0.017453293),#8);