appview/db: fix issues with collaborators table

- CollaboratingIn was not producing reverse mappings
- collaborators.created was never set

Signed-off-by: oppiliappan <[e-mail]>

appview/db/collaborators.go

···
 }
 
 func CollaboratingIn(e Execer, collaborator string) ([]Repo, error) {
-	rows, err := e.Query(`select repo_at from collaborators where did = ?`, collaborator)
+	rows, err := e.Query(`select repo_at from collaborators where subject_did = ?`, collaborator)
 	if err != nil {
 		return nil, err
 	}

appview/db/db.go

···
 				repo_at text not null,
 
 				-- meta
-				created text default (strftime('%y-%m-%dt%h:%m:%sz', 'now')),
+				created text not null default (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
 
 				-- constraints
 				foreign key (repo_at) references repos(at_uri) on delete cascade