GroupChats limited to 20 participants

[jazzz]

Problem

Adding more than ~20 participants causes groups to become corrupted.

Reproduction

Machine A: Basecamp 0.2.3-RC1
Machine B: Basecamp 0.2.3-RC1, + 20 Lurker bots

Machine A adds members via Basecamp ~5 at a time.
Upon reaching 20-25 members.
Basecamp members start showing different member counts and can no longer reach consensus.

[jazzz]

@osmaczko My best guess is that the DeMLS timer configuration is too short which is leading to a deadlock - at just over 20 users the stewards cannot process the proposals fast enough before all members abandon the freeze state due to inactivity.