prepare backend for snapshots, as requested in https://github.com/vatesfr/xo-web/issues/95 and https://github.com/vatesfr/xo-web/issues/96
add host action for https://github.com/vatesfr/xo-web/issues/97
add revert action for snapshots
handle message deletion
Bumps version number.
Merge branch 'next-release'