(1) Create host H, template T1, template T2. Create applications with the same name in H and T2. Link T1 to H. Link T2 to T1. Observe template-updated.png. Templates are linked, but there is no application in T1 and H's application does not say it comes from T2. Items, triggers, and graphs are OK.
(2) Create host H, template T1. Create application A on T1, link T1 to H. Unlink T1 from H. Go to applications of H. Observe linked-application.png, even though T1 is no longer linked to T1.
(3) If a host's application comes from a template, the link to the template is shown in blue. It is gray in items, triggers, and graphs.
(4) Also, when creating an application it should not be possible to press "Empty" button to select no host.
Blocker, because in (2) the database gets corrupted.