bower jquery-ui - exported changes to a separate css file

I exported all changes to jquery-ui.css to a separate file, to be able to upgrade the vendor library more easiely.

Review carefully. I tested with the ldap settings and it looks good, but additional testing of other occurences of jquery-ui is appreciated.

cc @owncloud/designers @blizzz 

All the changes in here are ported to `core/css/jquery-ui-fixes.css`