Serialization of DMN Result in Process Engine

AT:

• DMN result should not be set as variable
  • possible backwards compatibility problem when update to new camunda version
  • result is only avaiable for output mapping or execution listeners that are attached to the business rule task
  • name of transient variable is "decisionResult"
• mapping of result / convenience functions:
  • mapping function is specified by "camunda:mapDecisionResult" attribute:
    • singleValue: TypedValue
    • singleOutput: Map<String, Object>
    • collectValues: List<Object>
    • outputList: List<Map<String,Object>>
  • default mapping is "outputList"
  • the result of the mapping is set as variable that name is specified by "camunda:resultValue" attribute
  • if "camunda:resultValue" is missing then the result is not stored
• DecisionResult should implement List and DecisionOutput Map interface to use it easy with EL
• change type of collect value to something that can be serialize (currently it is of type number which is abstract)