allow not only deleting but also changing time/date of events scheduled from a section

[Zhang Weiwu]

according to the answer to Question #106863, for events scheduled from a section, a user can change its description, resources, but cannot change its time nor date. This feature request it can be changed. This change may have concequences that only developers can tell if appropriate, for example, journal needs to be updated to reflect change of an event.

This is feature request is one step beyond #559403 and is only needed for convenience and filed for completeness. Because if #559403 can be done, the user can always "change" an event by deleting and adding a different new one. But this is filed anyway for completeness.