fix: wrong matching variable for selecting channel in SSA of channel_in_queue
added first simple unit test assertion tool that uses the property evaluator
- added unicast test
- added assertions to multicast test
added constants for message types
minor documentation changes
added support for multicast in Send
adapted to changed signature of Send
vehicles back to 5 for testing
fix: avoid overwriting of fluent handlers by equally named entities in python evaluation context. This used to cause problems for channels and sensors.