added style param to to get_thumbnail

You can now pass cover stretch or contain as style. The stylenames are
similar as in css background
reverted the config file
Improvements to Navigation Admin

Added Fontawesome 3.0
made foldericons change color onHover
added font-awesome for ie7
Merge pull request #140 from betaman/master

Adds style param to filemanager_get_thumbnail(), improves Navigation admin UI, and updates Font Awesome to 3.0