added ability to configure multiple panes around the map

added ability to configure multiple panes around the map using a "sidebar" design:
![image](https://cloud.githubusercontent.com/assets/200780/3606494/6caca972-0d37-11e4-880a-a458e21a2305.png)

added new widget type `contentPane` to enable loading a widget as a contentPane into one of the new panes.