model_utils: extract mclasses and mclassdefs from MProject and Mgroup

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
model_utils: collect mmodules in mproject and mgroups

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
model_utils: allow intro and redef mclasses filtering

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
Merge: Model utils

This pull request needs #522 to be merged.

Introduce some usefull services in model_utils for further uses in documentation tools.

Pull-Request: #523
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>