Add local time gem

[jdugarte]

Local Time makes it easy to display times and dates to users in their local time. Its Rails helpers render elements in UTC (making them cache friendly), and its JavaScript component immediately converts those elements from UTC to the browser's local time.

https://github.com/basecamp/local_time

[Dantemss]

I intend to hopefully rewrite this to make it optional, especially since non-English locales will need some adjustments that I do not know how to make.