Bootstrap 3 Glyphicons, timezone offset for date range, non-numeric indexes for selects

This is my first pull request so please offer any guidance.

I am not sure if you can cherry-pick pull requests. If not let me know if you would like any changes removed.

Changes:
* Added offset parameter to variable header for date ranges.
* Allow database and display value mapping in selects and multi-selects.
* Switched to bootstrap 3 glyphicons to fix arrow in date range selector.