Deletes every working time within the selected range.

When deleting only a part of a working time, it will either be cut off or split into two separate working times.

E.g.: Working time from 08:00 to 11:00 AM.

	Delete selected range from 09:00 to 10:00 AM.
	This will result in two new working times from 08:00 to 09:00 AM and 10:00 to 11:00 AM.