Pipelet: ...
  - _add_destination() && _add_source: now accepts options for no_fetch

  - _add_source(): pass options on to __fetch_source_destination() for no_fetch

  - __add_source(): on union creation for multiple sources:
    - use option no_fetch with this._remove_source() and _add_source()
    - overloaded __add_source() returns union instead of this to allow _add_source() to complete with union
    - stop overloading __remove_source()

  - _add_source():
    - add warning on __add_source() that may return a union
    - add ToDo for the returned value when union

  - Encapsulate.._add_source(): add options parameter
  - Encapsulate.._remove_source: add options parameter