Admin navigation remade.

+ Instead of a constantly changing bar for secondary level navigation,
  the navigation links are now placed in a sidebar, on the left. In this
  sidebar, at least one set of links exist. Each set is visually
  separated from the others. When accessing a deeply nested model, a set
  of links will be shown for each of the containers.

+ Fixed a bug when using .row-fluid containers around .thumbnails. This
  is a known Twitter Bootstrap bug. The CSS hack did not work. Solved
  with a snippet of JS code.

TODO: clean the excessive nav files.