MDL-77794 contentbank: fix plugin type language strings.

AMOS BEGIN
 CPY [type_contentbank,core_plugin],[type_contenttype,core_plugin]
 CPY [type_contentbank_plural,core_plugin],[type_contenttype_plural,core_plugin]
AMOS END

lang/en/plugin.php

@@ -126,6 +126,8 @@
 $string['type_calendartype_plural'] = 'Calendar types';
 $string['type_contentbank'] = 'Content bank';
 $string['type_contentbank_plural'] = 'Content bank plugins';
+$string['type_contenttype'] = 'Content bank';
+$string['type_contenttype_plural'] = 'Content bank plugins';
 $string['type_customfield'] = 'Custom field';
 $string['type_customfield_plural'] = 'Custom fields';
 $string['type_coursereport'] = 'Course report';