[158] Stop connections between certain objects via the 'Subsequent' relation

Although most of the cardinalities have been thoroughly defined it was
still possible to build combinations despite of them being syntactical
incorrect. These changes catch those combinations and don't allow them
to be connected.
The combinations are as follows:
1) Event	-> Merger	-> Event
2) AnyProcess	-> Merger	-> AnyProcess
3) AnyProcess	-> Merger	-> DecisionNotSpecified
Merge branch 'feature-158' into develop