Adjust json dump parameters after change done in 2d0cad2c

This is necessary after dropping json bundled in Flask in favor of using the
json Python standard library.

See the following links for the changes that are necessary to do:

- https://github.com/mitsuhiko/flask/blob/7a353a7d/flask/json.py#L114-L129
- https://github.com/mitsuhiko/flask/blob/7a353a7d/flask/app.py#L306
- http://docs.python.org/2/library/json.html#json.dumps
Import directly from flask_script

flask.ext.* is a mechanism added by Flask to provide a smooth transition
from the old flaskext.* to the new flask_* way to import Flask plugins.

For more information see
https://github.com/mitsuhiko/flask/blob/7a353a7d/flask/ext/__init__.py#L3-L15
Import directly from WTForms

Since its release 0.9.0, Flask-WTF won't import anything from wtforms, so
instead we import directly from WTForms.

Checked that importing directly from WTForms in this way is possible for
releases as old as 5 years ago.

See the following for further reference:

- http://stackoverflow.com/a/18297150
- https://github.com/lepture/flask-wtf/commit/dd43c08a
Import directly from flask_wtf

flask.ext.* is a mechanism added by Flask to provide a smooth transition
from the old flaskext.* to the new flask_* way to import Flask plugins.

For more information see
https://github.com/mitsuhiko/flask/blob/7a353a7d/flask/ext/__init__.py#L3-L15
Drop requirements.txt

Is misleading and serves to no purpose right now. Can be regenerated in the
future if necessary.
Additional cleanups
Resolve FIXME by adding a new DEBUG setting
Add view helper to refactor common behavior
Move jsonwrapper helper to the view helpers section
Docs cleanups
Docs cleanup: Remove unnecessary section in settings

This will improve a little the readability.
Docs: Move some stuff from README to docs
README: Alter note styling so GitHub can render it in a readable way
README: Rewrite and reduce the text to improve readability

The README should be short. We already have the docs for more extensive
explanations.
Cleanup and fix the template
Rearrange views code

Will ease further cleanups.
Add FIXME
Avoid having a view that choses which code to call
Remove other view that choses which code to call

There is a remaining view, but still not sure how to drop it.
Add setting to control if the web UI is enabled or not