This is a big one campers; Add initial support for treeview nodes.

This commit adds the following:

- Storage of server groups in the configuration database
- Creation of a default server group on in the database
- A mechanism for plugging in treeview node types
- A node type for server groups with:
  - Treeview display
  - Custom per-node javascript implementing a menu option/dialogue to add new groups
  - Custom per-node CSS to style the treeview node
- JSON formatted data in response to AJAX requests, including:
  - Success/failure indication
  - Error message
  - Extra info (e.g. stack trace)
  - The original request data
  - Additional return data, e.g. node ID and label etc.

web/pgadmin/static/css/overrides.css

@@ -15,6 +15,11 @@
     color: #fff;
 }
 
+.alertify .ajs-content {
+    padding-left: 0 !important;
+    padding-right: 0 !important;
+}
+
 /* iFrames should have no border */
 iframe {
     border-width: 0;
@@ -30,6 +35,13 @@ iframe {
     padding-left: 0;
 }
 
-.icon-servers {
-    background: url('/static/servers.png') 0 0 no-repeat !important;
-}
+/* Alert info panel */
+.alert-info-panel {
+    border: 2px solid #a1a1a1;
+    margin-top: 2em;
+    padding: 5px 5px; 
+    background: #dddddd;
+    border-radius: 5px;
+    height: 8em;
+    overflow: scroll;
+}