Allow multiple block times per day

[AWhetter]

I want to allow a site to be viewable during only a certain time slot in the day. This requires being able to set up two time slots of blocking in a day.

The easy way to implement this would be to add a toggle to flip the blocking schedule so that the times entered represent the time slot when a site is allowed to be viewed, rather than when it is blocked.

The more flexible way would be to allow any number of time slots to block in a day.