Better countdown handling

[cnowacek]

The countdown is pretty coarse….it will display 1 month to go when there are actually nearly two months…maybe this can be improved?

[liuhenry]

We're currently using the rails view helper to render the time on the server, but it may be a better idea to send over the unix expiration date, and use a javascript library like Moment.js to render the countdown on the client side.

However, we also probably want to modify the time thresholds to something like:
< 1 minute to 2 hours - show minutes (1 - 119 minutes)
2 hours to 3 days - show hours (2 - 72 hours)
3 days to 4 months (3 days - 120 days)
4 months up - show months

We don't want to use weeks, and it's unlikely that a campaign will extend into the 4mo+ timeline.

[liuhenry]

#201 merged