stub test classes for ParticipantsBridge and ChatBridge
 - try to write a test
 - write tests to chat bridge
Adding initial tests for ChatMessage and making it more structured
Tests for chat bridge structure

See https://github.com/ritzalam/bigbluebutton/wiki/Messages
Correct public message format tests and add tests for private messages
Pending ChatTranslateMessage tests
Beggining ParticipantBride tests
Correct translate message tests
Tests for participant events

UserJoined and UserLeft. Still missing some details like
meeting name and user externalID
Tests for WhiteboardDrawEvent rectangle