Custom checkboxes, improved toggleClass, bugfixes.

- Custom checkboxes to match the style of other input/select elements. Probably
  won't work in IE<9.
- toggleClass() now has an 'on' parameter, which explicitly states whether the
  class should be enabled or not. removeClass is now implemented as a call to
  toggleClass.
- Fixed typo that meant block_id was not being returned when searching across all blocks.