use short form bel when building term signature

fixes Selventa/sdp-cytoscape#14
kam node resolver fixes; close #57

api fixes:
- term signature is calculated in pure short form
- term parameters are retrieved in appearance from left to right in the Term
  to ensure proper sequence in UUID querying

refactor:
- added FunctionEnum.toShortestForm() to return either the abbreviation if
  non-null else the displayValue
- retain split implementations for Term's toBELLongForm() / toBELShortForm()
  for efficiency...the choice is only binary (i.e. short vs long form)
- centralized term parameter substitution into Term.toTermSignature()