Factor out MatrixClient methods to MatrixBaseApis
Starts work on a class which is intended to just wrap the Matrix apis with very
simple functions.
There is a lot more work to be done here. For now, I have just taken methods
which don't refer to anything in MatrixClient except _http. This excludes a
bunch of things which refer to $userId, as well as the login stuff because of
the deviceId stuff I've just added :/.
For now, it's an internal class. I don't really see any reason it can't be
exposed to applications, though.
