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.
