1. Add v2_alpha URL back in, since things seem to be using it.
2. Don't reject the request if the device_id in the upload request fails to
match that in the access_token.
We should now be able to get our device_id from the access_token, so the
device_id on the upload request is optional. Where it is supplied, we should
check that it matches.
For active access_tokens without an associated device_id, we ought to register
the device in the devices table.
Also update the table on upgrade so that all of the existing e2e keys are
associated with real devices.
This tracks data about the entity which made the request. This is
instead of passing around a tuple, which requires call-site
modifications every time a new piece of optional context is passed
around.
I tried to introduce a User object. I gave up.
This follows the same flows-based flow as regular registration, but as
the only implemented flow has no requirements, it auto-succeeds. In the
future, other flows (e.g. captcha) may be required, so clients should
treat this like the regular registration flow choices.
Removes device_id and ClientInfo
device_id is never actually written, and the matrix.org DB has no
non-null entries for it. Right now, it's just cluttering up code.
This doesn't remove the columns from the database, because that's
fiddly.
