API break at interfaces for SerializableTreeMap/DualKeyMap

* Renamed SerializableMapId to SerializableMapKey
* Renamed SerializableMapDualId to SerializableMapDualKey
* Renamed functions to get Keys for SerializableMapKey and
  SerializableMapDualKey to avoid conflics with implementator's
  use of id() and primary/secundary_id () functions/properties.