Use local timezone, allow users to close events, and a bonus bugfix.

The original intent of the timezone stuff was to mimic the manual live update threads where users would generally timestamp their updates with a provided timezone.  In retrospect, this was likely just due to the limitation of being static text and not actually that helpful to viewers.  Now that moment is in place, it's possible to do this, so user-local timestamps it is!  The separators had to be made client-side only because some timezones vary from UTC in partial hours which would mutate where the separators go.

In the backbonification, I accidentally made the time separators use the older update's hour. This is incorrect because the older update was usually some time *after* the hour started and so the separator was in the wrong place entirely.  The fix included here brings back the correct placement.

Finally, I've added rudimentary support for closing events. This updates the UI for viewers appropriately. A new permission is added since it's a rather drastic ability as well.

:eyeglasses: @chromakode @umbrae