Create form to add reservation

[acrollet]

Let's place an 'Add Reservation' button on nodes with booking enabled. It should go to a form that allows choosing the start and end dates, (and times for hourly) defaulting to the current date and a day/hour (daily/hourly) later. After a user submits the form, we should:

• ensure there is availability for at least one unit associated with the current node (if not, prevent submission and show an error to the user)
• if there's availability, save an event, linked to the first available unit, authored by the logged in user, in the 'Booked' state.

[acrollet]

@cecrs leave your feedback here :)

[cecrs]

@acrollet comment updated