nitdoc_next

Some improvments on Nitdoc.

* better handling of projects in namespaces
* page for each MGroup/MProject
* page for each MProperty
* better display of concerns tree + ranking stub
* reviewed presentation for M*Def
* reviewed presentation for page headers
* "all classes" sidebar on MModule pages
* fix menu height and responsive features on menu
* general cleaning

Beta can be found [here for stdlib](http://gresil.org/jenkins/job/CI-nitdoc/ws/doc/stdlib/index.html) and [here for nitc](http://gresil.org/jenkins/job/CI-nitdoc/ws/doc/nitc/index.html).

Fixes: #400, #485 and #534.