Issue #31 : Adding a friendly message for the user in case the Node location is not correctly configured

A new dialog will be shown to the user if the node location is not correctly configured. Clicking on 'Open Preferences' will directly take the user to the preferences page.

Sample dialog shown to the user - 

![image](https://f.cloud.github.com/assets/2890490/493116/545a7992-bb1e-11e2-9aff-612cee7c3ad2.png)