Merge: Ini of projects

Now that projects can have metadata, let's just provide them.

Commits are grouped by maintainer and directory so that selfish maintainers can review only their.

Fell free to propose better tagging or metadata. See #1655 and http://nitlanguage.org/nep/project_metadata.html for current state of the discussion.

Note that the proof on concept of a catalog is available at http://nitlanguage.org/catalog

Pull-Request: #1675
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>