plugin XEP-0384: Fully reworked to adjust to the reworked python-omemo: - support for both (modern) OMEMO under the `urn:xmpp:omemo:2` namespace and (legacy) OMEMO under the `eu.siacs.conversations.axolotl` namespace - maintains one identity across both versions of OMEMO - migrates data from the old plugin - includes more features for protocol stability - uses SCE for modern OMEMO - fully type-checked, linted and format-checked - added type hints to various pieces of backend code used by the plugin - added stubs for some Twisted APIs used by the plugin under stubs/ (use `export MYPYPATH=stubs/` before running mypy) - core (xmpp): enabled `send` trigger and made it an asyncPoint fix 375

Those certificates are used to activate TLS for end-2-end testing (to be as
close as possible as production environment), they are used in other containers
needing TLS certificates (notably Prosody).

To generate them, minica has been used. Minica can be found at https://github.com/jsha/minica.

The following commands have been used:

$ minica --domains "server1.test,*.server1.test,server2.test,server3.test,libervia-backend.test,libervia-web.test"
$ chmod 0644 minica.pem server1.test/cert.pem && chmod 0640 server1.test/key.pem

Note that certificates are valid for 2 years and 30 days, so they must be renewed after this delay.