For some reason trailing/leading underscores were allowed when uploading
files. But the rest of the code (eg. listing or downloading files) never
supported this. This patch removes this special case for uploading files
to streamline ID cleaning of pages and media files.

The uploader now just strips a bunch of common special chars. This is
not a complete cleanID() implementation. A full clean is done
server-side on uploading.

IE8 can't substr() with negative offsets.

this fixes another IE javascript problem in edit mode

A trailing comma created an empty array item causing IE8 to choke.

To avoid problems when an AJAX request takes a bit longer in the ACL
manager, a throbber is shown while loading the info.

Translators need to add another string.

i needed to disable all plugins to figure out which plugin was causing
template error, so it was quite annoying to click on the tiny checkbox

added html label so i could at least click on the plugin name to toggle
checkbox state

fixed resizing mediamanager panels in Chrome using browser sniffing (FS#2351) - any better solution welcome

as per commit 34bc7405

paraphrased '<' character in some language files (en, de, de-informal) to avoid XML errors -- please fix other languages

re-added font-size to .ui-widget of jqueryui theme to make programmatical removing of font-family easier

fix widths of panels in fullscreen mediamanager to be 100% when resizing (FS#2351) -- please test in different screen sizes, etc