Greyson Parrelli 45c4eafbd7 Add the ability to block groups.
This also fixes the situation where we block group-leave messages,
preventing blocked contacts from leaving groups.

Fixes #7970

Also, this forced us to upgrade libsignal-service, which fixes the
websocket timeout issues. Thanks to @dpapavas!

Fixes #6644
2018-09-18 15:26:50 -07:00
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