Support msisdn registration and signin (#384)
* Functionality for msisdn signin
* Add methods to request tokens from synapse to do msisdn
verification
* Extend interactive-auth to work with m.email.identity (which
is significant since email auth is quite a chunk more complex).
* Oops, fix merge
* Fix lint
* Add submitMsisdnToken
* Support the bind_msisdn param to register
Change the bind_email flag to an object with keys 'email' and
'msisdn', backwards compatibly.
