Improvements for K-Fêt CMS.

K-Fêt - Wagtail
- Page content becomes a StreamField.
- GroupTeam snippet becomes a block for stream field.
- Navigation menu moved becomes a "flatmenu", preventing possible future conflicts.
- Page layout can be modified in wagtail admin.

K-Fêt
- Add shorthands for ukf account balance/article price.
- Cleaning stylesheets and templates.

kfet/cms/static/kfetcms/css/editor.css

@@ -0,0 +1,18 @@
+.snippets.listing thead, .snippets.listing thead tr {
+    border: 0;
+}
+
+.snippets.listing tbody {
+    display: block;
+    column-count: 2;
+}
+
+.snippets.listing tbody tr {
+    display: block;
+}
+
+@media (min-width: 992px) {
+    .snippets.listing tbody {
+        column-count: 3;
+    }
+}