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
(1) Yes, adding now

(2) When I run this, all three figures open at once (approximately), do you get them sequentially (having to close one before the next opens) or do you mean something different?