Add message threads #394

This new view sorts the messages by threads based on the reply_to.
Now we store only the message which started a new thread in the reply_to
field to avoid recursive queries.

app/assets/stylesheets/bootstrap_and_overrides.css.less

@@ -484,3 +484,35 @@ i.package.icon-only {
   padding-right: 6px;
   padding-left: 7px;
 }
+
+// TODO: Remove the .panel defines after updating Bootstrap to >=3.0
+.panel {
+  margin-bottom: 20px;
+  background-color: #fff;
+  border: 1px solid transparent;
+  border-radius: 4px;
+  -webkit-box-shadow: 0 1px 1px rgba(0, 0, 0, .05);
+  box-shadow: 0 1px 1px rgba(0, 0, 0, .05);
+}
+
+.panel-default {
+  border-color: #ddd;
+}
+
+.panel-heading {
+  padding: 10px 15px;
+  border-bottom: 1px solid transparent;
+  border-top-left-radius: 3px;
+  border-top-right-radius: 3px
+}
+
+.panel-default > .panel-heading {
+  color: #333;
+  background-color: #f5f5f5;
+  border-color: #ddd
+}
+
+.panel-body {
+  padding: 15px;
+  padding-bottom: 0px;
+}