Shift object

A time model contains the defined shifts. Shifts are required to execute relative events. Shifts must not overlap, and must be defined within the limits of the equipment's cycle.

Shifts are displayed on a grey background in the table view.

`Create shift`	Creates a new shift.
`Create break`	Creates a new break during the shift.
`Delete shift`	Deletes the selected shift, including all related breaks.
`Help`	Activates online help.