Specify the timezone on upload

This PR has code changes to allow someone to specify the timezone on upload.  Right now it is functional, but ugly.  The hope is that design work can be done to make it pretty and/or change how the picking is done.

This depends on the cheddar/utc branch  of in-d-gestion.  Given that said branch hasn't been merged yet, the only way to run this locally is to use npm link.  Once the cheddar/utc branch is merged (https://github.com/tidepool-org/in-d-gestion/pull/30), this PR needs an update to its package.json dependency. 

@kentquirk @jh-bate LMK what you think