Updated visualization for single lens.

Changes:
- Updated to use new mainWFS.py which has the lenslet array for the numerical solution
- Improved plot aesthetics
- Removed SingleLens.py which is no longer needed
- Attempted to improve readability and modularity
I have googled as much as I can on this and I don't see anything about how to prevent figures from showing up one at a time using the event ghost interpreter.  

I tried using the subplot feature instead such that all three would end up in the same window showing something that looks like the picture I attached.  But I am not sure if this is an improvement because the aspect ratio of the combined image is quite awkward.
![subplots](https://cloud.githubusercontent.com/assets/7480692/3344000/15896432-f8a6-11e3-8f8a-356bf1053b70.png)