Add Wagtail CMS for kfet app.

K-Fêt
- Integrate wagtail to serve "static" pages of old K-Fêt website
- Fixture "kfetcms/kfet_wagtail_17_05" contains a copy of old website
(as in May 2017).
- Media files can be got until end of June 17 at
http://partage.eleves.ens.fr//files/604e6dea2ceebc66b1936c6b3f911744/kfet_media.tar.gz

Login/logout
- Update package django_cas_ng to last version.
- Clean COFCASBackend.
- Change CAS version to 3 (version used on eleves.ens). This enables
the logout redirection (for CAS ofc).
- Add messages and clean existing ones on login/logout (for both
outsider and cas users).

Misc
- Update settings to bypass an incompability between debug-toolbar and
wagtailmenus packages.
- Better management of dev/test-specific urls (if debug-toolbar wasn't in
INSTALLED_APPS, media files were not served).
- UI improvements.

kfet/cms/static/kfetcms/css/index.css

@@ -0,0 +1,155 @@
+.cms-content {
+    text-align: justify;
+    font-size: 1.1em;
+}
+
+@media (min-width:768px) {
+    .cms-content {
+        font-size: 1.2em;
+        line-height: 1.6em;
+    }
+}
+
+.cms-column {
+    column-gap: 45px;
+
+    padding: 20px 15px;
+    background: white;
+}
+
+@media (min-width: 768px) {
+    .cms-column {
+        padding: 35px 30px;
+    }
+}
+
+@media (min-width: 992px) {
+    .cms-column {
+        margin: 0 15px;
+    }
+}
+
+
+/* Titles */
+
+.cms-content h2, .cms-content h3 {
+    clear: both;
+    margin: 0 0 15px;
+    padding-bottom: 10px;
+    border-bottom: 1px solid #c8102e;
+    text-align: left;
+    font-weight: bold;
+}
+
+@media (min-width: 768px) {
+    .cms-content h2, .cms-content h3 {
+        padding-bottom: 15px;
+    }
+}
+
+/* Paragraphs */
+
+.cms-content p {
+    margin-bottom: 20px;
+    text-indent: 2em;
+}
+
+.cms-content p + :not(h2):not(h3):not(div) {
+    margin-top: -10px;
+}
+
+@media (min-width: 768px) {
+    .cms-content p {
+        padding-bottom: 15px;
+    }
+
+    .cms-content p + :not(h2):not(h3):not(div) {
+        margin-top: -30px;
+    }
+}
+
+
+/* Lists */
+
+.cms-content ol, .cms-content ul {
+    padding: 0 0 0 15px;
+    margin: 0 0 10px;
+}
+
+.cms-content ul {
+    list-style-type: square;
+}
+
+.cms-content ol > li, .cms-content ul > li {
+    padding-left: 5px;
+}
+
+
+/* Images */
+
+.cms-content .richtext-image {
+    max-height: 100%;
+    margin: 5px 0 15px;
+}
+
+.cms-content .richtext-image.left {
+    float: left;
+    margin-right: 30px;
+}
+
+.cms-content .richtext-image.right {
+    float: right;
+    margin-left: 30px;
+}
+
+
+/* Team groups & members */
+
+.team-group {
+    margin-bottom: 20px;
+}
+
+.team-group .col-btn {
+    margin-bottom: 20px;
+}
+
+.team-group .member-more {
+    display: none;
+}
+
+.team-member {
+    padding: 0;
+    margin-bottom: 20px;
+    min-height: 190px;
+    background-color: inherit;
+    border: 0;
+}
+
+.team-member img {
+    max-width: 100%;
+    max-height: 125px;
+    width: auto;
+    height: auto;
+    display: block;
+}
+
+.team-member .infos {
+    height: 50px;
+    margin-top: 15px;
+}
+
+@media (min-width: 768px) {
+    .team-group {
+        margin-left: 20px;
+        margin-right: 20px;
+    }
+
+    .team-member {
+        min-height: 215px;
+    }
+
+    .team-member img {
+        max-height: 150px;
+    }
+}
+