Previously we would only clear the publicKey since that was the only attribute,
but now we should delete the entire record. This method is currently only called
from tests.
// FREEBIE
This will enforce that all identity record attributes are valid and present
before allowing the record to be saved. This is necessary since we will be
exposing a lower-level method to save an identity with explicit values for
firstUse, nonblockingApproval, and verified status.
saveIdentity is now reponsible for determining firstUse, so we must not remove
the existing key before updating it.
Previously, the implementation provided an extra check against overwritting an
existing key, but that should be done via isTrustedIdentity instead.
// FREEBIE
Bind a single listener to keychange events from the storage interface,
which then looks up relevant conversations and adds notices to them,
with tests.
Previously we would need to instantiate a conversation model in order to
start listening to its key change events. In practice this usually
happens at startup but we shouldn't rely on it, and it incurs higher
overhead since it creates a different listener for each conversation.
// FREEBIE
Previously if there was no session to remove, the promise returned from
removeSession would never resolve, potentially blocking sending for that
recipient until restart.
// FREEBIE
