With lots of reference points, the current sorting by distance is really
not usable.  Sorting by name allows to more easily find a given refpoint
in the list.

While we're at it, display the distance in the dropdown menu so that it's
easier to check if it's the right refpoint.

Starting from Django 1.9.11, ALLOWED_HOSTS is also taken into account when
DEBUG is turned on.

See https://docs.djangoproject.com/en/1.10/releases/1.9.11/#dns-rebinding-vulnerability-when-debug-true

This fixes an issue with recent browsers that do not seem to correctly get
the CSRF token from a variable, resulting in 403 responses for AJAX
requests.

This reverts commit eaaeb5ad.

This reverts commit 48f4dca3.

Use "requests" to avoid compatibility issues with urllib/urllib2 between
python2 and python3.

Also add more validation about what api.geonames.org might return.

This fixes issue #23 related to mixed HTTP/HTTPS content, because
api.geonames.org is not available over HTTPS for free-of-charge usage.

This also has the advantage of defining a generic interface, so that we
can support other sources of altitude data with different formatting
(e.g. IGN) without changing the javascript code.

While we are at it, also cache the result of API calls in Django.  This
will avoid hammering on the real API server if our javascript code is too
enthusiastic.

Proxying has a slight disadvantage: if the API server performs
rate-limiting based on IP address, then we will reach the limit much more
quickly.  This is because all requests will now come from the celutz
server, instead of from each individual client broswer.

validation de la recherche de lieu avec la touche enter + positionnement auto du curseur sur le champ de recherche

Link update_map with draw_image (simplify lot of thing + more logical...) + place window.onload after the initialization of the leaflet variable. All together should fix issue #18