* 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
* s/QueryBackfill/PerformBackfill/g
* OutputEvent now includes AddStateEvents which contain the full event of extra state events
* Only include adds not the current event
* Get adding state right
* 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
* Consolidation of roomserver APIs
* Comment out alias tests for now, they are broken
* Wire AS API into roomserver again
* Roomserver didn't take asAPI param before so return to that
* Prevent roomserver asking AS API for alias info
* Rename some files
* Remove alias_test, incoherent tests and unwanted appservice integration
* Remove FS API inject on syncapi component
