[MERGE] calendar,web: update to FullCalendar v4 & fixes

This merge updates the FullCalendar library from v3 to v4.

The purpose of this update for us is to add proper support of the
drag-and-drop of events on mobile.

But also to fix scrolling issues present mainly on smaller screens. In
those configurations multi/inner-scrolls were present resulting in
either the inability to properly scroll the desired content or even
blocking altogether the scroll.

As a nice-to-have feature, version 4 removes its dependency on the
jQuery library, allowing faster loading of a bigger set of events.

Last but not least, this version also reduces its dependency on the
Moment.js library (but still keeps a binding to it for compatibility
purpose).

In addition to the update of the library itself, this merge adapts the codebase
to the library's API changes and extracts some methods and templates to allow
further customization of the calendar view.

Finally, a couple of fixes are also applied :
* time-based instead of ID-based order of events in month view
* unwanted transformation of time-based events into all-day events in month view

Task ID: 2092550

closes odoo/odoo#48630

Related: odoo/enterprise#9554
Signed-off-by: Pierre Paridans <pparidans@users.noreply.github.com>