MDL-42711 theme port from LM: forum layout on small screen devices

This is a backport of MDLSITE-2445.  Wrapping the 'Started by' and 'Last post'
texts helps. On smaller device, these two get smaller font too. This is far
from optimal but better than the current (default) behaviour.

theme/bootstrapbase/less/moodle/modules.less

@@ -9,11 +9,51 @@ select {
     width: auto;
 }
 
+// Forum
+
 .path-mod-forum .forumheaderlist,
 .path-mod-forum .forumheaderlist td {
     border: none;
 }
 
+.path-mod-forum .forumheaderlist {
+    thead .header {
+        white-space: normal;
+        vertical-align: top;
+    }
+    thead .header.lastpost {
+        text-align: right;
+    }
+    .discussion {
+        .author, .replies, .lastpost {
+            white-space: normal;
+        }
+        .replies {
+            text-align: center;
+        }
+        .topic, .topic.starter, .picture, .author, .replies, .lastpost {
+            vertical-align: top;
+        }
+    }
+}
+
+@media (max-width: 979px) {
+    .path-mod-forum .forumheaderlist {
+        thead .header {
+            font-weight: normal;
+            font-size: round(@fontSizeSmall);
+        }
+        .discussion {
+            .author, .replies, .lastpost {
+                font-size: round(@fontSizeSmall);
+            }
+            .replies .unread a {
+                padding: 0;
+            }
+        }
+    }
+}
+
 .forumpost {
     .well;
     padding: 6px;