Remove references to SQL/database material

We're not teaching SQL/databases.
Update README.md
Add agenda to home page
Add useful links
Add proper install instructions
Reorganize guides & links
Add line break below "setup"
Update olson.r.html
Remove line breaks under "agenda" and "setup"

They look crappy.
Add the vignettes back in
Update links for NumPy and plotting sections
Fix NumPy and plotting links in agenda
Merge remote-tracking branch 'rhiever/gh-pages' into mit

Bring in Randy's changes, restoring some lost content.

Conflicts:
	README.md
	_includes/people/olson.r.html
	index.html
	lessons/vignettes/Numerical_analysis_with_NumPy.ipynb