MAGN-4937 As a user I would like to get feedback on if the Dynamo is processing something

The change is to have some kind of progress indication on the RUN button to indicate Dynamo is executing the graph.

After this fix, when the RUN button is clicked, a circular progress bar will be displayed on the run button (see image). The RUN button will be in disabled mode (without RUN text on it). Upon completion, RUN button will get its actual state. 

@elayabharath  had advised me the color of the progress bar , as well as its location.

- [ ] @pboyer 
- [ ] @lukechurch 

![image](https://cloud.githubusercontent.com/assets/8495197/5286475/a275fbca-7af2-11e4-9a53-fe78017e89c3.png)


I'd recommend putting an attribution here:  http://www.codeproject.com/Articles/49853/Better-WPF-Circular-Progress-Bar