Add support for filtering hosts by primary user

[thehesiod]

Here's how I did it: farmersbusinessnetwork@4c87e9b

[thehesiod]

btw, looks like the name of the search box doesn't change if you click search by ID or now by primary user. Perhaps instead the title should be query, or removed.

[thehesiod]

btw, another thing missing for all of these search pages is wildcard support

[chief8192]

That whole search widget is definitely less that ideal, and is something that we hope to replace if we overhaul the admin UI.

[thehesiod]

ok going to add another feature request: sorting by column :)

[thehesiod]

closing this in favor of #24