Better events for deletion of team conversations

[fisx]

Start sending conversation.delete event also to all team members (whether in the conversation or not). team.conversation-delete will still be sent as before.

This solves the following issue:

One side effect of getting only one of the team.converation-delete and conversation.delete events is that we can't display who deleted a conversation in a team. The team.converation-delete event doesn't contain the from field.

Also, lots of small refactoring.

[fisx]

galley
  Galley integration tests
    Teams API
      [...]
      delete team conversation:                  FAIL (3.28s)
        test/integration/API/Teams.hs:742:
        unexpected notification received: (0,Notification {ntfId = 6f6fe025-d3d0-11e9-8001-901b0e95d6e0, ntfTransient = False, ntfPayload = List1 {toNonEmpty = fromList [("conversation",String "6dd7e926-89fc-4c4c-9944-89430923582b"),("time",String "2019-09-10T13:39:38.776Z"),("data",Null),("from",String "02ce384a-fd6e-46f9-a1ab-d0a3a86b8e41"),("type",String "conversation.delete")] :| []}})

If I go to line 742 in test/integration/API/Teams.hs and try to pluck another conversation.delete event from either of the 3 web socket handles, I get different errors:

        Exception: Timeout: No matching notification received.

or

        Exception: Timeout: No matching notification received.
        Match failure: expected: d5696a08-b18b-40d9-8296-07ba27d73a15
         but got: a05af6e5-4baf-476e-a3fa-8f9973d4db39

[tiago-loureiro]

Looks good to merge assuming it passes CI tests