Split weekly event button [1237350]

[texcoffier]

This wish applies also for daily events.

Creating weekly events is great to create events,
but in some case they are unusable after because
each week a different resource may be used.

It should be nice to have in the "edit event" window
a new button next to "new" and "delete"
named "split".

If the user click on split then the current
weekly event in splited in multiple "no repeating" event.
Each one of the "no repeating" event is initialized
with the resources of the initial weekly event.

A more powerful interface can use a hierarchical menu
with the following choices:
* Split all the days
* Split in 2 :
** From start to XX/XX/XX included
** From start to YY/YY/YY included
** ...
* Extract this day (create exception and add apointment:
** XX/XX/XX
** YY/YY/YY