Bug 7351 : feature that allows to delete a range of dates

Bug 7351 : feature that allows to delete a range of dates

Four new options, one for single holidays, one for the repeatable holidays.
One to create exceptions on a range of dates, one to delete exceptions in a range of dates.
Note that the exceptions are not deleted if you delete a range of repeatable dates.
But if you delete a range of single holidays the exeptions inside will be deleted.

Signed-off-by: Stephane Delaye <stephane.delaye@biblibre.com>
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>