* Add PerformInvite and refactor how errors get handled
- Rename `JoinError` to `PerformError`
- Remove `error` from the API function signature entirely. This forces
errors to be bundled into `PerformError` which makes it easier for callers
to detect and handle errors. On network errors, HTTP clients will make a
`PerformError`.
* Unbreak everything; thanks Go!
* Send back JSONResponse according to the PerformError
* Update federation invite code too
* Pass join errors through internal API boundaries
Required for certain invite sytests. We will need to think of a
better way of handling this going forwards.
* Include m.room.avatar in stripped state; handle trailing slashes when GETing state events
* Update whitelist
* Update whitelist
* Add missing routing for PerformDirectoryLookupRequest
* Tweak output
* Fix some bugs in devices
* Don't default to federated room joins in response to invite
* Update sytest-whitelist
* Update comments
* Return correct room ID from PerformJoin
* Fix appservice and EDU server API setup, update sytest-whitelist
* Update sytest-whitelist
* Add PerformJoin template
* Try roomserver perform join
* Send correct server name to FS API
* Pass through content, try to handle multiple server names
* Fix local server checks
* Don't refer to non-existent error
* Add directory lookups of aliases
* Remove unneeded parameters
* Don't repeat join events into the roomserver
* Unmarshal the content, that would help
* Check if the user is already in the room in the fedeationapi too
* Return incompatible room version error
* Use Membership, don't try more servers than needed
* Review comments, make FS API take list of servernames, dedupe them, break out of loop properly on success
* Tweaks
