Develop a matrix-communities Connector for Opsdroid

[Cadair]

Post the Events support, we should move all the community handing out into its own connector. This could do a bunch of polling to emit events when things in the community change, and react to events like "AddRoomToCommunty" etc to modify the community.

Given the very-beta state of communities in matrix, I would recommend this be a separate plugin for opsdroid and not included in core with the main matrix connector.