explicitSave option for dashboard

This feature allows the client code to decide if saving should be continuous or if it should be explicitly handled externally from the dashboard (either by a user action like clicking a save button as in the demo, or programmatically by some external logic).

I have updated the demo in this branch with a new route `/explicit-saving`. Here are screenshots from it:

![image](https://cloud.githubusercontent.com/assets/1390651/3002871/ed0ab828-dd46-11e3-9923-838824362a57.png)
![image](https://cloud.githubusercontent.com/assets/1390651/3002881/10acd7d4-dd47-11e3-9eb4-e18181cf9c96.png)