Implement MatrixClient.getStoredDevicesForUser which uses
Crypto.getStoredDevicesForUser, which is more powerful than listDeviceKeys, and
isn't deprecated.
Also a couple of accessors for DeviceInfo.
A couple of small refactors which fell out of the aborted stuff for upgrading
to secure Ed25519 keys, but are useful in their own right.
The main functional change here is to calculate the "algorithms" list from
DECRYPTION_CLASSES (and hence include megolm in the list).
It is possible for `room` to be null when passed to
MegolmEncryption.encryptMessage; we need to avoid dereferencing it. Instead,
make sure that the EncryptionAlgorithm knows about the roomId it is targeting,
and use that.
Replace the increasingly-long argument list on the EncryptionAlgorithm
constructor with a params list, and update DecryptionAlgorithm to match.
- to make way for alternative encryption algorithms. We now store an encryption
object for each room, rather than referring to sessionstore on each event.
Also a little light tidying to the jsdocs.
