Author: Andrew Nicols
MDL-59920 calendar: Allow user to choose if deleting one or all events
http://git.moodle.org/gw?p=moodle.git;a=commit;h=2dbfb484aa81be5191f05b8cfab7f46c117226c1
http://github.com/moodle/moodle/commit/2dbfb484aa81be5191f05b8cfab7f46c117226c1
+ 3.4 en [confirmeventseriesdelete,core_calendar]
+ 3.4 en [deleteoneevent,core_calendar]
+ 3.4 en [deleteallevents,core_calendar]