Use static_url and route_url

This PR makes uses of `request.static_url` and `request.route_url` in the `ngeo.html` Mako template. In this way we create correct URLs when using `pserve` as well as when using Apache `mod_wsgi`. It also makes it possible to use [Chache Busting](http://docs.pylonsproject.org/projects/pyramid/en/master/narr/assets.html#cache-busting) and  ["multi-domain" URLs](https://github.com/camptocamp/c2cgeoportal/blob/master/c2cgeoportal/lib/__init__.py#L83-L105).

@fredj, I plan to make a PR to `pyramid_closure` for that as well. Does it makes sense to you?
It is the file system path that you pass to `static_url` (and `static_path`), not a logical name. `geoportailv3:static/` is just a way to refer to the `static` dir relatively to the package directory. We can't just the same thing in the case of `node_modules` because `node_modules` is outside the package directory. So we the full system path.