Add "local" time for events

[jmfee-usgs]

One option is system time, since that informs the user based on their computer time zone settings.

Another option for large events with a losspager product is:

https://earthquake.usgs.gov/realtime/product/losspager/ci38457511/us/1562429005114/json/event.json

which has pager['local-time-string'] in it. You could use that if you like.

[vinceq-usgs]

FYI Got yet another user requesting this feature for the DYFI page. There's a "Local system time" for the Latest Earthquakes page, but I don't think that setting gets stored?

[jmfee-usgs]

@dslosky-usgs : this could be a good issue for the relative time component. I think a shared component for times would be useful.

This should take a time input, and can have a couple formatting options (UTC, System Time, Relative Time).