Added restriction for dashboards and metrics #2:)

Please, find my comment to commit.
I have already test it and add some instructions for you.
Same comments as above apply here as well. Also note that this view is cached (see L61 to L68) and a cache hit will bypass your permission check. A possible solution would be to include the user ID in the cache key.

You're also doing a SQL query inside of a double for loop, which can lead to a big performance issue when you have a large number of metrics and restrictions. Instead, you should:

* compute a list of metric names (`names = [series.name for series in data]`)
* identify which metrics have restrictions (`restrictions = UserMetric.objects.filter(name__in=names).values_list('name', flat=True).distinct()`)
* when you have restrictions, fetch the current user's permissions and remove forbidden series from the dataset.