Fix inline dialog for inline dialogs

jQuery.remove also removes all click events from the dom-object.
jQuery.detach preserves them.
This way the e.g. "Add another Media Object" for the gallery plugin works again.
Tested with django 1.5.5
Fix "+" image in CSS for file upload button

given that ui.css resides in /your-static-path/media_tree/css/ui.css and
the image resides in /your-static-path/admin/img/tooltag-add_over.gif
the fix is valid.
Tested with django 1.5.5.