Business hours

Added conditional logic during `fc-slot` row creation to see if the time slot being created is outside the business hours (provided as additional options, `startOfBusiness` and `endOfBusiness`). 

If the current row is outside the business hour range, it adds the `fc-non-business-hours` class to the slot, which is an additional CSS class with `background-color:rgba(230, 230, 230, .8);`

This CSS rule should probably be changed since the `rgba` syntax doesn't work on IE or older browsers, but wasn't sure how to approach that issue.