Cleanup

There's a lot going on here, so let me explain:
-- I began cleaning up some of the lesson 1, 2, and 3 slides, which is where those edits came from.
-- I took the fall schedule off the front page, and moved the devops blurb to the top of the page
-- Replaced 'view page source' with 'edit on github'
-- Updated the headcount chart, and took it off the site (it looks messy and is sad).
-- Added some onboarding newbie docs, which will hopefully be improved. 
-- Added the rest of the exercises to the exercises page. 

@jordane @ElijahCaine @edunham @iankronquist   I can push these once they look good to everyone. 
`$ man git` also gives a quick overview of all other git commands, which can be useful for finding new things.