views: keep the list of towns ready to serve
views: keep the list of towns ready to serve

It's quite heavy to process, mostly on the serialization part, and we
have plenty of RAM.

It lets "login_required" and "roles_accepted" do their job, but then the
result is the same for all users, computed only once.

Caching at the HTTP level would make it tricky to invalidate the cache
when we update the list of towns, and cache headers would only prevent a
single user from calling this endpoint too often.

openmaraude/APITaxi,openmaraude/APITaxi