Draft: SMGOptionalObject: allow colored optional
Allow optional objects from colored regions as they are needed in SMGState#isLessOrEqual -> SMGJoin#constructor -> SMGJoinSubSMGs#constructor -> SMGJoinValues#constructor -> SMGJoinValues#insertLeftObjectAsOptional (the failed assertion stack trace, basically).
Refactor: use SMGObject's id instead of the local field; use the target object's label instead of generic one.
Add tests for lists with samely colored elements. For now, SMG timeouts, as it cannot abstract these lists (i.e. --smg-ldv is effectively --smg for colored lists). At least we don't fail on these tests now.