Upgrade to reCAPTCHA v2

reCAPTCHA v1 has been shut down since March 2018.

We now uses reCAPTCHA v2:
- user must check a simple checkbox (No CAPTCHA),
- eventually he must validate a challenge.

Moving keys settings allows to use the captcha for development.

Fixes #192.

gestioncof/templates/demande-petit-cours-raw.html

@@ -7,7 +7,7 @@
 {% if success %}
 <p class="success">Votre demande a été enregistrée avec succès !</p>
 {% else %}
-<form id="demandecours" method="post" action="{% url "gestioncof.petits_cours_views.demande_raw" %}">
+<form id="demandecours" method="post" action="{% url "petits-cours-demande-raw" %}">
     {% csrf_token %}
     <table>
     {{ form | bootstrap }}