Multiple jails navtree, storage and plugins modifications

- Remove plugin fetching from navtree, moved it to jails

- Add request object to freeadmin tree nodes so that nav objects can
  access it

- Remove dead code from jails admin

- Modify jails forms to understand when a jail is passed or not, this
  allows the forms to be used in navtree context with a jail specified
  or generic context with no jail specified.

- Implement minimal filter() method for Jails model. Also add str() and
  unicode() methods to model.

- Implement nav menu for jails, including jails configuration, jail
  configuration, plugins and storage configuration.

- Update jails urls to make jail id optional in storage matching

- Update jail views to reflect optional jail id url matching

- Update plugin install url to require a jail id

- Update plugin install view to reflect required jail id

- Remove dead plugin code from services nav

- Update plugins list page to view storage options

- Update plugins rc script to not need force modified, everything is
  handled by the warden now