Determine timezone offset for date_taken using latitude and longitude gh-54 gh-293

[jmathai]

Uses the tzwhere and pytz libraries to get the string representation of the location (i.e. US/Pacific) and converts that to an offset which is used to adjust the date related parameters when organizing files.

• [ ] Include tests for updating date_taken when changing time or location via update

Addresses gh-54 and gh-293.