Set up client-side development environment

This PR sets up the client-side development environment. There's still a lot to do, but this is a start.

At this stage, both `buildout` and `make` need to be run:

```shell
$ ./buildout/bin/buildout -c buildout_elemoine.cfg   # install eggs, substitute vars in ini files
$ make build  # upload node deps, build js and css
$ make compile-catalog  # compile the i18n catalog
```

Now `pserve` can be run:

```shell
$ ./buildout/bin/pserve --reload development.ini
```

And open [http://localhost:5000/ngeo](http://localhost:5000/ngeo) or [http://localhost:5000/ngeo?debug](http://localhost:5000/ngeo?debug) in the browser to see the basic ngeo-based page.

Things to do:

* Move stuff to c2cgeoportal scaffolds (we probably want to that much later)
* Remove `buildout` and rely on `make` only
* Set up Travis
* Upload `pyramid_closure` to pypi instead of using a `find-link`'ing to github
* Rely on openlayers's or ngeo's `tasks` scripts instead of having our own copies

@sbrunner, pay attention to the `closure_library_path` and note that I need to execute a Python command to set its content. It is similar to `authtkt_secret`.

I think this PR should be merged, and that we should build/improve upon it.

PS: je viens de réaliser que j'ai écrit ceci en anglais. Trop tard !
should be `elemoine` :-)