https://github.com/element-hq/matrix-react-sdk/pull/92 changed the default mode
for encryption to throw an error when sending a message and the room contains either:
- a verified user with an unverified device
- a verifeid user who has changed their identity.
We're not really ready for this (we lack the UI to deal with it), so roll that
back.
Add a labs option which will, when set, switch into the "invisible crypto"
mode of refusing to send keys to, or decrypt messages from, devices that have
not been signed by their owner.