modelbuilder: get_mmodule_by_name get a mgroup as context

Signed-off-by: Jean Privat <jean@pryen.org>
modelbuilder: search_module_in_paths return ModulePath

Instead of a simple String

Signed-off-by: Jean Privat <jean@pryen.org>
modelbuilder: split `search_mmodule_by_name` from `get_mmodule_by_name`

Signed-off-by: Jean Privat <jean@pryen.org>
modelbuilder: use qualified name in imports to import things

    import foo::bar

Signed-off-by: Jean Privat <jean@pryen.org>
test: test qualified importations

Signed-off-by: Jean Privat <jean@pryen.org>
nitunit: updade usage of get_mmodule_by_name

Signed-off-by: Jean Privat <jean@pryen.org>
Merge: Qualified import

Enable `import foo::bar`

Pull-Request: #391
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>