mdSidenav service breaks when sidenav is placed inside an ng-view

[ivan7237d]

In my app the right sidenav is only required for one of several views, so is placed inside that view. Initially mdSidenav('right') works correctly, but stops working if one switches to another view and then returns to the one with the sidenav.

From looking at source, it seems like the issue occurs because when destroyed, a sidenav does not deregister itself from $mdComponentRegistry, so after a new sidenav is created, $mdComponentRegistry.get keeps returning the old instance.

[pandaiolo]

Duplicate of #473, fixed by #531 (not merged yet)