Add support for converting between time zones

[scattana]

Suggested contribution: add support for timezone conversion.

Example use case: an organization running events in multiple time zones.

Right now, it appears events default to UTC, but if a device's time zone setting is different, the time is automatically converted. A helper function could be added to convert time appropriately if a different time zone parameter is passed (following this or a similar format: http://www.timezoneconverter.com/cgi-bin/zonehelp.tzc?cc=US&ccdesc=United%20States)