MDL-10604:

Add ability to add sub categories directly from category screens.

lang/en_utf8/moodle.php

@@ -36,6 +36,7 @@
 $string['addresource'] = 'Add a resource...';
 $string['address'] = 'Address';
 $string['addstudent'] = 'Add student';
+$string['addsubcategory'] = 'Add a sub-category';
 $string['addteacher'] = 'Add teacher';
 $string['admin'] = 'Admin';
 $string['adminbookmarks'] = 'Admin bookmarks';