* Refactor Matrix event listener in Mjolnir and ManagedMjolnir.
closes https://github.com/matrix-org/mjolnir/issues/411.
Issue #411 says that we have to be careful about room.join,
but this was before we figured how to make matrix-appservice-bridge
echo events sent by its own intents.
* Remove MatrixClientListener since it isn't actually needed.
* Protect which config values can be used for ManagedMjolnirs.
* Introduce MatrixSendClient
so listeners aren't accidentally added to a MatrixClient instead
of MatrixEmitter.
* doc
* Move provisioned mjolnir config to src/config.
This just aids maintance so whenever someone goes to change the config
of the bot they will see this and update it.
* doc for matrix intent listener.
