1.2 keyword references (#50)
1.2 keyword references (#50)

* Add UseTrackable trait

* Add use in Content Type and Media

* Refacto UseTrackable to use generic addReferenceToEntity and removeReferenceToEntity

* Add UseTrackable::isUsed

* Update UseTrackable::getUseReferences to allow context selection

open-orchestra/open-orchestra-mongo-libs