Show appropriate wording for appointments that have already started

@alexbotsford noticed last night that the front page shows "..in 9 minutes" for appointments that started 9 minutes ago but have yet to end.

This changes the time display to remove the prefixing "in" and add a suffix of "from now" for future appointments and "ago" for appointments that have already started.

![screenshot 2014-03-05 08 48 55](https://f.cloud.github.com/assets/202/2334311/4c015ce6-a477-11e3-8da9-9aee80c82db4.png)