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
So this isn't a `DateParser`, because that would parse a `Date`. This thing parses *two* dates for some reason, and it doesn't return anything.