Less confusing timestamps for message views

[justinvdm]

We display timestamps like April 30, 2015, 8:19 a.m, but I think that is UTC time. To avoid confusion, we either need to show explicitly that it is UTC time (April 30, 2015, 8:19 a.m UTC), or show the time relative to the user (April 30, 2015, 10:19 a.m for a user in SA, for example).

The latter approach seems more common, but I think the first approach might more sense in our case: since people might be communicating times that messages were sent or received, it is useful and less confusing for them to be seeing the same time in the UI.