RAAML11 — Add a Causality association class which extends simple Causality association

Sometimes the transition from one situation to another situation needs additional properties which cannot be captured by a simple association. The common solution for that is to use an association class to express causality allowing for additional properties to be added to the transition. This pattern is already used in the STPA method. The proposal is to create a general pattern so other methods can access this capability. This would include creating an association class on the common core Situation.