Merge changes Ib27f6974,Ic6065991,Ic8aab523,Ifc70a042,I1306e493 into stable-2.16

* changes:
  TaskAttributeFactory: Consistently cache predicates
  task: Remove unthrown exception
  TaskAttributeFactory turn more Exceptions into INVALID tasks
  plugin:task Adds support for names-factory of type change
  Add support for tasks-factory and names-factory keywords