Feature: Make new booking modal to be client side

[DonKoko]

Okey so we want to make the modal for new booking client side, however we still want to keep the route. Let me sum up the tasks:

• Create a client side modal for new booking
• When clicking the "New booking" button on bookings page, open the client side modal
• Add a "New booking" button on calendar page, that will also open the client side modal
• Keep the route bookings/new so if someone navigates to it in the browser it still works

We might have to create a bunch of functions that handle both the loader and the action for new booking as we would need to have 2 routes: the current booking.new and a resource route that doesn't return HTML but just JSON.

Let me know if there are any questions.