E2EE OMEMO support

Can you add OMEMO?

• https://github.com/Syndace/python-omemo
• https://github.com/Syndace/python-twomemo
• https://github.com/Syndace/python-oldmemo

Note that it can be removed:

• https://github.com/Syndace/python-omemo-backend-signal

Thanks in advance.