Added time zone support

Closes #2 

Added timezone support to the stats screen.  Until the shared iOS repo has a lightweight data model to support passing values around, a parameter was added to the view controller, stats service, and stats remote service init methods.  This time zone will need to be set when creating the services but it is allowed to be nil on the view controller (defaults to system timezone).

Opted to not keep the view controller's original init method signature to force consumers of the library to update their code to remain functional.  Not following site timezone is broken behavior.