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

libsrc/leddevice/schemas/schema-dmx.json

@@ -5,6 +5,7 @@
 		"output": {
 			"type": "string",
 			"title":"edt_dev_spec_outputPath_title",
+			"default":"/dev/ttyUSB0",
 			"propertyOrder" : 1
 		},
 		"rate": {
@@ -18,13 +19,6 @@
 			"title":"edt_dev_spec_delayAfterConnect_title",
 			"default": 250,
 			"propertyOrder" : 3
-		},
-		"rewriteTime": {
-			"type": "integer",
-			"title":"edt_dev_spec_rewriteTime_title",
-			"default": 5000,
-			"append" : "ms",
-			"propertyOrder" : 4
 		}
 	},
 	"additionalProperties": true