Refactoring to support multiple grid sizes.
Added 16 and 24 column grids.
Merged base into grid partial.
Added optional grid column overrides.
Added 12 and 24 column overrides.
Various issues.

* Fixed issue with override CSS re-applying base cell styles.
* Renamed 'cell-X-hide/show' classes to 'show/hide-X' to avoid
  name collisions with base cell styles.
* Refactored show/hide styles to not apply 'display: block' to
  elements that were originally inline.