See discussion on https://gerrit.wikimedia.org/r/#/c/278081/3/resources/mobile.references/references.js

Basically we should not need to use trackSubscribe in anyway.
We should pass a ReferenceGateway to the ReferenceDrawer and no code inside references.js should need to think about the display of references inside the drawer.

• ReferencesGateway class created
• ReferencesDrawer is passed an instance of ReferenceGateway
• When binding to sups inside the content area, to display a reference we invoke ReferenceDrawer::showReference