cmd: CMD option for port number of gogs web to prevent first time run conflict

- routers: use new binding convention to simplify code
- templates: able to set HTTP port number in install page

modules/setting/setting.go

@@ -178,7 +178,7 @@ func NewConfigContext() {
 			log.Fatal(4, "Fail to load custom 'conf/app.ini': %v", err)
 		}
 	} else {
-		log.Warn("No custom 'conf/app.ini' found, please go to '/install'")
+		log.Warn("No custom 'conf/app.ini' found, ignore this if you're running first time")
 	}
 	Cfg.NameMapper = ini.AllCapsUnderscore