close #257

The npm configuration:
- Includes linting of javascript with eslint

The webpack setup here:
- Bundles javascript and css, using hashing to support server-side
  caching, with support from Flask-Webpack and
  manifest-revision-webpack-plugin
- Uses babel to transpile ES6 javascript
- Includes a development server with hot-replacing of javascript and
  css code

Use the new FLASK_DEBUG environment variable
which is standard as of Flask 0.11, in order
to control the use of dev or prod config.

Need to set this anyway, in order for "flask run"
to use reloader and no concurrency.

- Update Flask to 0.11 (with built-in Click integration)
- Remove manage.py
- Add autoapp.py per Flask doc's new recommendations
  for using Click with an app factory
- Define cookiecutter-flask's commands in cli.py
- Register shell context and shell commands as part
  of factory-based app creation
- Update README instructions with examples for running
  commands in new Click style