Simplify QML handling: Relax constraints that all dimensions must be from same contract type. Maybe even remove contract type concept (probably not needed in EMF models with ids, only useful for textual syntax?)

Relax constraints to avoid the following validation error that occurs if one dimension is added to a contract which is not in the contract type:

Diagnosis of de.uka.ipd.sdq.dsexplore.qml.declarations.QMLDeclarations.impl.QMLDeclarationsImpl@1efe846{platform:/resource/BRS Optimisation Tactics/QMLDefinition_1_NoCon/PCMProfile_BRS_1_graphicalOnly_3D_NoCon.qmldeclarations#__FjEYJyKEd-NNcIT2kpSGQ}
The 'all_DIMENSIONs_must_be_from_same_CONTRACTTYPE' invariant is violated on 'de.uka.ipd.sdq.dsexplore.qml.contract.QMLContract.impl.SimpleQMLContractImpl@a8ec02{platform:/resource/BRS Optimisation Tactics/QMLDefinition_1_NoCon/PCMProfile_BRS_1_graphicalOnly_3D_NoCon.qmldeclarations#_FqNZYaCrEd-s9uTaURbrKAIn}'