This pull request properly sets the events EventJoinLeave and EventTopicChange for messages from the RocketChat bridge and drops messages which are neither one of those events nor plain messages.
For an unknown reason we get duplicate messages (from the same channel)
using the realtime API when we have > 1 channel subscribed on.
Solution for now is caching the message ID in a LRU cache and ignoring
the duplicates.
This should be reviewed when we have actual editing support from the
realtime API
* Add support for editing/deleting messages
* Add support for uploading files
* Add support for avatars
* Use the Rocket.Chat.Go.SDK
* Use the rest and streaming api
Currently fully support mattermost,slack and discord.
Message deleted on the bridge or received from other bridges will be
deleted.
Partially support for Gitter.
Gitter bridge will delete messages received from other bridges.
But if you delete a message on gitter, this deletion will not be sent to
other bridges (this is a gitter API limitation, it doesn't propogate edits
or deletes via the API)
