Make tests pass upgrading to Flask-WTF 0.9+

This PR makes tests pass by upgrading and forcing Flask-WTF 0.9+  (see`https://flask-wtf.readthedocs.org/en/latest/upgrade.html#version-0-9-0):

- import from ``wtforms``instead of `flask.ext.wtf`
- use ``WTF_CSRF_ENABLED`` setting instead of `` CSRF_SETTING``
- fix ``db.Text`` field convertion (there may be a more generic solution)