more efficient implementation of toList, toOptList and flatten
change feature model parameters for consistency

avoid automatic prefix guessing by name
allow loading of small and full feature model both by fexpr and dimacs
check that small fexpr model is implied by full model
increase test coverage in ConditionalLib and Conditional
simplify code
cleanup and refactoring of CDeclUse code for readability
eliminate someDefinition and someImpliedDefinition calls in CDeclUse

This is extremely expensive for performance and is computed even when not
needed at all. Used lots of SAT calls to detemine whether a struct
was defined in a specific context (and only exactly in this context,
which likely does not work correctly in many cases)
Rewrote the code to consider the context when
the struct is undefined. New code does not use any SAT call.

Passes test cases, but not sure that it's actually equivalent.