fixes #6519 - updating associations UI

Added associations to the UI:
+ subscriptions to content hosts and activation keys
+ activation keys to content hosts

This is oddly formatted to me.  Maybe do this instead:

```javascript
$scope.activationKey.$promise.then(function () {
    ActivationKey.contentHosts({id: $scope.activationKey.id, 'organization_id': CurrentOrganization}, 
        function (response) {
            $scope.contentHosts = response.results;
            $scope.table.working = false;
        }
    );
});
```