Check deploy keys when Gogs is run with Service.RequireSignInView=true (#4078)

* Check deploy keys when Gogs is run with require_sign_in_view

Check if the deploy key can access to a repository. A deploy key
doesn't represent an gogs user, so in a site with Service.RequireSignInView
activated we should give read access only in the repositories where
this deploy key is in use. In other case, a deploy service or system
using an active deploy key can get read access to all the repositories
in a Gogs service.

* Refactoring: Comments starts in a new line

* Minor change in a comment

* Code cleaning. Replace spaces with tabs

modules/setting/setting.go

@@ -806,6 +806,10 @@ func newWebhookService() {
 	Webhook.PagingNum = sec.Key("PAGING_NUM").MustInt(10)
 }
 
+func NewService() {
+	newService()
+}
+
 func NewServices() {
 	newService()
 	newLogService()