Extended Appearance Interface for Shared Themes Support

When a theme is installed, it will not automatically apply to windows with root privileges unless it is located in /usr/share/themes. Today, this means a manual command line (sudo) copy of the theme to the shared location.

A neat solution would be to divide the theme selection window into two sections, say "My themes" and "Shared themes". Themes from /usr/share/themes will be found under the "Shared themes" category, while personally installed themes will be under "My themes". When a theme under "My themes" is selected, a button for sharing the theme will become available. Clicking it should bring up a PolicyKit authorization after which the theme is automatically moved to /usr/share/themes. It will now be located under "Shared themes" instead of "My themes". Likewise, when selecting a theme under "Shared themes", a button will allow for the theme to be unshared, again using PolicyKit authorization.

This would allow for windows with root privileges to be themed without command line work, as well as provide users with an interface for sharing themes with each other (provided it is authorized).

This proposal comes as a result of the discussion here: http://ubuntuforums.org/showthread.php?t=742917