Add separate boolean keys for each day of the week:

    "working-day-monday"
    "working-day-tuesday"
    "working-day-wednesday"
    "working-day-thursday"
    "working-day-friday"
    "working-day-saturday"
    "working-day-sunday"

These are much easier to decipher and much easier to bind boolean
GObject properties to.

The "working-days" setting is now deprecated.