Add Reservation to Rentr

* Users can create reservation dates
* Users can not create invalid reservation date ranges
* Users can view their reservations for a particular listing
* Users can view all of their reservations
* Users can view all their reservations for a listing if any exist
* Guests can still use app
Still not thrilled about doing one query for each date in the range.

Can we select the number of dates in the database that are within the range (one query, with `count`), and check whether that number is equal to the number of dates in the range?