Added mobile CSS to exams-table (#333)

Author: k499wang

public/assets/sass/mixins/_exam-bank-table.scss

@@ -4,6 +4,12 @@
   text-align: left;
   border-collapse: collapse;
 
+  @media only screen and (max-width: 980px) {
+    display: block;
+    overflow-x: auto;
+    -webkit-overflow-scrolling: touch;
+  }
+
   @mixin match-filters($filter-classes) {
     tbody {
       tr:not(#{$filter-classes}) {