Added mockito to lib-folder.
Abstracted most of the code of 'PropertyToNestingBinding' into a more general 'NestingObserver' and implemented tests for that class.
Restructured inheritance of nesting builders.
Renamed methods to create 'NestingObserver'.
Implemented nested listeners (including tests and demo).
The  methods 'ObjectPropertyNestingBuilder.nest' and 'ObservableValueNestingBuilder.nest' now both call '....nestProperty'.
Finished Javadoc.
Minor changes to Eclipse settings.