Internal Constraint representation & MM cleanup

* Add an InternalConstraint representation that can be used by decoders
  and for an input constraint transformation from DSML-based
  constraints.
* Remove the unused old DSL meta model.
* Remove the common constraint meta-model and move the Period and
  Deadline constraint model into the MOEA MM.

Issue-Ref: 3279
Issue-Url: https://af3-developer.fortiss.org/issues/3279


Signed-off-by: Alexander Diewald <diewald@fortiss.org>