Use Bootstrap 3.1 because PyScss is currently broken for 3.2.0.

See https://github.com/Kronuz/pyScss/issues/287
Set up scss asset compilation.

* Downgrade Flask-Assets due to
  https://github.com/miracle2k/flask-assets/pull/78
* Switch to rjsmin as it is bundled with WebAssets
* Add definitions for twbs-font-path and twbs-image-path to keep PyScss
  from complaining
* Log *everything* to the console for manage.py
* Give the logger a decent formatter
Run CSS through minifier when not in debug mode.
Binding to the root logger interferes with Flask's logging somehow.