I updated the active links system by creating a templatetag `is_active`.
The issue was that the old system was unable to parser several  endpoints. Now
it's possible to specify as many endpoints as required by their related
name (defined in the `urls.py` file. This system is a bit more
cumbersome than trying to just active a link according to its base
directory but the advantage is that if you change the endpoints in the
`urls.py` file you won't have to update the template.

Signed-off-by: Matthieu Berjon <matthieu.berjon@inria.fr>