Allow unique validator to use context + set booking PK as composite (date + user_id)
Do not allow duplicate entries per day, per user:
 * Fixing Unique Validator to work with objects as foreign keys,
 * Pass filtered input to InputFilter,
 * Adding functionality to Hyrdators to hydrate dates,
 * Add User Strategy to fetch user for Booking objects
 * Fixing controllers and services
 * Update Tests
Merge pull request #8 from WeareJH/fix-duplicate-entry-issues

Do not allow duplicate entries per user per day