improve serial hotplug (#389)

* - disable device when error indecates that the problem is not solvable on reconnect
- introduce a preOpenDelay of 2 seconds (currently value is hardcoded)

* rs232:
- make preOpenDelay available via webui
- fix preOpenDelay
- add basic usb serial detection

* - revert 3819ae7
- fix schema files

* make json checks compat with utf8+bom

* make shutdown effect a bit more flexible

effects/shutdown.json

@@ -6,6 +6,8 @@
 		"speed"            : 1.2,
 		"alarm-color"      : [255,0,0],
 		"post-color"       : [255,174,11],
-		"shutdown-enabled" : false
+		"shutdown-enabled" : false,
+		"initial-blink"    : true,
+		"set-post-color"   : true
 	}
 }