Move media library directory filter to filters toolbar.

This is the "replacement" for the tree view directory browser which
was removed to get rid of the Yahoo JS dependency.

References #30
Introduce secondary netbook breakpoint; move some styles there.

References #58
Switch karma plugin options to core config groups.

The karma plugin had its own solution for config option groups in
tabs which didn't work well with the refactored 2.0 backend. We
have a solution for config groups in the core; it now uses this
for better backend consistency.

References #54
try to fix - draft preview non-object error

Draft previews threw:
Fatal error: Call to a member function assignByRef() on a non-object in /fullpath/include/functions_entries.inc.php on line 1235, which is the $serendipity['smarty']->assignByRef('entries', $dategroup); line.

Please double check if that is gone now.