MDL-66488 mod_assign: make submission comments textarea expandable

Allow submission comments textarea on assignment "View all submissions"
page to expand both ways, rather than just vertically.

mod/assign/styles.css

@@ -182,6 +182,10 @@
     background-color: #fc9;
 }
 
+.path-mod-assign .gradingtable .commentscontainer .comment-ctrl .comment-area textarea {
+    resize: both;
+}
+
 .path-mod-assign td.submissioneditable {
     color: red;
 }