Adds client timezone offset to date range requests. Closes #23

@mailbackwards can you review this and see if it is what you had in mind. TZ management is a bit quirky b/c we need to depend on the client for determining timezone. So, it passes the offset determined by the client and uses that to adjust the query time range. At the same time, we want the client inputs to display the local time, so the unadjusted times are passed back.