Better config

Simplifies configuration and consolidates it into a single file. The goal is to simplify reasoning about the state of configuration, and more clearly show what changes are made for each environment.

I would appreciate feedback from @charltonaustin, @jacksingleton, and @Hainish on this one! Note that this PR isn't quite done yet - I uncovered an interesting issue with cookies that merits further investigation before merging.
I think that you want this to be 
FlaskConfig.DEBUG = True