Merge: nitweb: add graphs stubs

Add some very simple graphs tabs to nitweb:

* Packages: http://nitweb.moz-code.org/package/popcorn
* Groups: http://nitweb.moz-code.org/group/popcorn%3E
* Modules: http://nitweb.moz-code.org/module/core::array
* Classes: http://nitweb.moz-code.org/class/core::Array

Pull-Request: #2174
Reviewed-by: Istvan SZALAÏ <istvan.szalai@savoirfairelinux.com>
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Arthur Delamare <arthur.delamare@viacesi.fr>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>

diff --cc src/web/web_base.nit
Simple merge