Allows using unpublished queries in alerts

[alison985]

fixes #2659

This is a port of Mozilla fork functionality upstream.

Original PR commentary is here: mozilla#97 where Arik specifically said that unpublished queries are excluded from the Dashboard Add Widget dialog on purpose. Therefore, we only added unpublished queries to the alert search.

[arikfr]

Actually, the same reasoning I mentioned for Add Widget applies here as well. Basically draft queries are not supposed to be used anywhere, to make sure people publish them and not keep them in this state forever.

Unless there is a very good reason for allowing draft queries in alerts, I don't think we will merge this in...

[arikfr]

Closing this for now. Let's re open if there is a reason to change this behavior.

[emtwo]

@arikfr, suppose we wanted to make this into an extension for the Mozilla fork. I imagine we could use the Policy object from here #2560 to check if the object passed into Query.search() should have the include_drafts attribute.

This would be a small change in this codebase here to allow the attribute to be added if the policy (only turned on in the Mozilla fork) allows it. In other words, we would only be adding the "extension point" here.

What do you think of this?