add custom listenbrainz url support and make ui "consistent"

Co-authored-by: spezifisch <spezifisch@users.noreply.github.com>
Co-authored-by: Alex McGrath <amk@amk.ie>

server/ctrladmin/ctrl.go

@@ -122,6 +122,7 @@ type templateData struct {
 	//
 	CurrentLastFMAPIKey    string
 	CurrentLastFMAPISecret string
+	DefaultListenBrainzURL string
 	SelectedUser           *db.User
 }