Disappearing timer changes in message history

[BaeoMaltinsky]

I'm inclined to make this a UI detail rather than a persistent feature of a linear message history. If you have secrets worth hiding, then not having a record of having turned them on or off seems correct.

If we go this route, this can stay confined to libherald, if we don't and make them persistent, then there are a number of questions I would like to have answered about how these are going to be handled (e.g., are these events searchable in the global message search).

[GallagherCommaJack]

Any persistent record of deleted messages is something we should avoid wherever possible.

[colleenm]

Agree with Jack, I prefer no record in message history.

I don't know what "make this a UI detail means"--do you mean we only show what the current timer setting is set to somewhere in the client UI? (That's what I think we should do)

[kaavyajayram]

++ Changes regarding expiring message disappear with the messages