[ENH] Calendar: Register an event as new from an old one on calendar mode

Create a new calendar event from an existing one from Calendar.

Steps to test:

With calendar_fullcalendar disabled:

1. In tiki-calendar.php ensure that you're in Calendar View if not, click on 'Calendar view' button
2. On the calendar click on specific event you want to modify.
3. On the tooltip click on 'Save as' icon.
4. Make the various changes and save.

With calendar_fullcalendar enabled:

1. Activate calendar_fullcalendar
2. In tiki-calendar.php ensure that you're in Calendar View, if not click on 'Calendar view' button
3. On the calendar click on specific event you want to modify.
4. On the modal check 'Save as' input.
5. Make the various changes and save.