Resolve "BUG: admins sending messages disables disappearing message timer"

Closes #356 (closed)

bugfix

• SYMPTOM: admin sending message with disappearing message set to any non-zero value will turn disappearing messages off (always)
• CAUSE:
  • for whatever reason, signald now relays normal text messages with the expiresInSeconds fields incorrectly set to 0
  • this was triggering dispatcher.detectUpdatableExpiryTime to think it was handling a setExpiry message (when in fact it was not)
• FIX:
  • modify detectUpdatableExpiryTime to exclude any message with a non-empty body or attachments fields for consideration as an expiry time udpate message (which works b/c since all true expiry time update messages have empty bodies)

dependency udpate

match upstream master signald build (as of 2020-10-25 | MR 29):

• upstream MR: https://gitlab.com/thefinn93/signald/-/merge_requests/29
• upstream commit: https://gitlab.com/thefinn93/signald/-/commit/4d5ea9ff49574bedffec2418d7b5168e0663017b
• team-friendo MR: signald-fork!24 (merged)
• team-friendo commit: signald-fork@6735f6a9
• current as of: 2020-10-25
• current signald container tag: 1.0.12

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