If the other party have already sent us their mac, see
if we can send a reply and do so if possible

This reverts commit 20b2f8a6.

We still have some crashes with HTTP/2

Adapt to cm-verfication-event API changes

Don't force HTTP/1.x so that if the server supports
HTTP/2 libsoup shall use it.

HTTP/2 in libsoup2 doesn't like the stream being read in a
different thread, which is what the JsonParser does. Instead,
read the stream ourselves and feed it to the JsonParser so
that we can enable HTTP/2 support again.

This handles device key verification.
Currently only single device verification is implemented.

'signatures' and 'unsigned' members should be removed from the json
as per the spec

display_name and avatar are not room-member specific, and so
use cm-user API to set those details so that it works for
cm-account too