django debug toolbar only used in development mode

but since the app crashes without it, it's simpler to just have it
in the main requirements.txt file.
tightened up setup instructions based on today's experience
Remove debug_toolbar from being required
Thou shalt not import unused things
Restore debug toolbar to dev reqs then
Merge branch 'setup' of github.com:18F/foia-hub into setup
Merge pull request #376 from 18F/setup

Updates setup instructions