Added JSON API Support to the Media controller

fixes #344 medias pages do not show error messages

fixes #236 - Installation media are now usable with more than one operating system.

Ensure that all index views and controllers are consistent

Ensures that all controllers use @search in the index method
Ensure that all index views use pagination

removing show action in places it doesn't make sense, and minor visual changes

fixes #202 - Remove activescaffold from the medias page

fixes #151 - add show host page
Added a nested link to hosts to lots of controllers

Added some more text to the settings menu, removed some fields which are not yet required.

• Fixed an issue when the host arch is not the last part of the directory.
  • introduced the $arch variable in the media path value
• Added default media values for CentOS 5.3 and Fedora 11

fixed an issue with wrong contoller names which lead to broken links, redid some model relationships (hopefuly simplified - hence removed the nested_has_many_through plugin