Complete migration to platform-client for API calls

**NOTE**: this is dependent on https://github.com/tidepool-org/platform-client/pull/9

See `platform-client` PR linked above for more details on migration.

This PR also completes data model change where messages where tied to a `teamId` but are now tied to a `userId`.

I've tested this locally (creating accounts, profiles, uploading data, visualizing data, etc.) and things seem to work fine.