admin: Rewrite list templates

Implement the following changes:
* **Decoupling of class-based views (Djano-eztables) from urls:** There
  is only one url (/admin/json/<?type>) which multiplexes various
  class-based views. Fix apyrgio/synnefo#54.
* **Rewrite the skeleton for list templates:** With the
  Django-eztables plugin, there is no need to provide the html for table
  rows, therefore these should be rendered obsolete. Note, for the time
  being only the user page works with the new skeleton. Fix apyrgio/synnefo#53.
* **Rename all instances of "index" to "list":** Fix apyrgio/synnefo#52.