changed the participant id. Now, it's the hash of the public key of the participant. this was necessary since the id has to be verifiable using the private key.
Added the localParticipant to the class since it's needed in the decrypted messages after the id is not randomly chosen anymore.
Cleaned up a lot because it's not necessary now to create the participant by an URL. this will later be needed (and probably a little bit complicated to implement...).
Had to change the tests after a change of the participant api.
Cleaned also up these tests.
Deleted since not needed anymore. The ids are now generated as a digest of the public key.