change all plt to pyplot

also renamed module 4 lessons to add prepended module number for
consistency across modules.  all notebooks have been run for
presentation
Merge pull request #116 from numerical-mooc/pyplot

change all plt to pyplot
Merge https://github.com/numerical-mooc/numerical-mooc into numerical-mooc-master

Conflicts:
	lessons/01_phugoid/01_02_Phugoid_Oscillation.ipynb
	lessons/01_phugoid/01_03_PhugoidFullModel.ipynb
Merge branch 'numerical-mooc-master'