ni_nitdoc: Get all classes of a module

Addign a function to regroup all classes of a module and it associate
their state like introduced or refined

Signed-off-by: Stefan Lage <lagestfan@gmail.com>
ni_nitdoc: adding classes column in modules page

Generate classes column for each modules page

Signed-off-by: Stefan Lage <lagestfan@gmail.com>