Remove duplicated js file
Validate reservation on creation time

* Avoids creating reservations with no valid occurrences
* The form is now sent via ajax
* Alert dialog popups on failure
Post-merge fixes (semicolons, wording)
Show loading dialog, clear jstorage before redirect
Fix AJAX in 3-step-booking, remove non-ajax case

The case where the form would be submitted without switching to AJAX
would only happen with an old firefox version and a rarely used
extension, so it wasn't really necessary.
Only intercept certain exceptions when booking

anything that's not a NoReportError while creating a booking is probably
an actual error which should be logged as an error and not just shown to
the user as "you can't create this booking because..."
Send a JSON response on booking modification
Proper error handling for AJAX requests

jsonify_errors did not care about XHRs with a non-json payload
Avoid colliding occurrences during modification

We must not synchronize occurrence data from the old occurrence on the
same day as this would un-cancel auto-cancelled occurrences.