Improve layout and CSS.  Fix List-Category-Item assignment

- Fix List-Category-Item assignment
  - use FancyListCategory instead of list/category IDs
  - FancyListCategory is submitted by form and passed into URLs/views
  - This include assigning items
- Move inline styles to application.css
- Categories resize depending on screen size, to minimum of 300px
- Remove defunct add/remove_list from Category model