add getters for namespace of LDevice/LN

It could be found using OCL but is needed for NSD validation

created merge request !47 (merged) to address this issue

By Dominique Marcadet on 2019-05-30T13:17:56 (imported from GitLab project)

mentioned in merge request !47 (merged)

By Dominique Marcadet on 2019-05-30T13:17:57 (imported from GitLab project)

closed via merge request !47 (merged)

By Dominique Marcadet on 2019-05-30T14:56:38 (imported from GitLab project)

mentioned in commit 0fb2fa80

By Dominique Marcadet on 2019-05-30T14:56:38 (imported from GitLab project)