Added sign in and registration using SQLAlchemy and Flask-User

(Using pre-existing templates)

Also got rid of /patients for now, since that can just be /
We're [following](https://hammerlab.atlassian.net/wiki/display/MSL/Software+Development#SoftwareDevelopment-Python) the Google Python style guide, which says you should [be consistent](https://google-styleguide.googlecode.com/svn/trunk/pyguide.html?showone=Strings#Strings) about single vs. double quotes in a single file. I usually go with single quotes everywhere, but either is fine.