Implement initial API
Created by: rjw57
Implement an initial API for submitting preferences. Anyone can query the API for the preference of an individual user or all users. Queries may be filtered by user, bounded by "expressed at" times and/or ordered by "express at" times.
A signed-in user my update their preference by POST-ing a new preference to the preferences endpoint. The preferences endpoint only allows listing he most recent preference for any user although all past preferences are recorded.