MDL-60249 assign: resize quickgrade textareas

The Bootstrap CSS reset prevents horizontal resizing of textareas. We want to allow it in the quickgrading ui.

mod/assign/styles.css

@@ -56,6 +56,10 @@
     padding: 0;
 }
 
+.path-mod-assign textarea.quickgrade {
+    resize: both;
+}
+
 .path-mod-assign .gradingbatchoperationsform .mform fieldset {
     margin: 0;
     padding: 0;