Added isExpired to Slots so I can tell the difference between things which are not editable and things which are in the past
Rejigged the CSS classes generated by the template and updated the css.  Slots you can manipulate have a box, slots that you can't dont.  Slots that are in the past are greyed out, slots that are not, are not.
Fixed bug in convertToDay function - I was rounding in a 12 hour clock rather than a 24 hour one.