Allow definition of additional glob patterns for serial ports

Configuration happens via config.yaml, just add additional patterns by listing them under serial > additionalPorts, e.g.

    serial:
        additionalPorts:
        - /dev/myCustomPort
        - /dev/myOtherCustomPort

octoprint/settings.py

@@ -32,7 +32,8 @@ default_settings = {
 			"detection": 0.5,
 			"connection": 2,
 			"communication": 5
-		}
+		},
+		"additionalPorts": []
 	},
 	"server": {
 		"host": "0.0.0.0",

octoprint/util/comm.py

@@ -45,6 +45,11 @@ def serialList():
 			   + glob.glob("/dev/tty.usb*") \
 			   + glob.glob("/dev/cu.*") \
 			   + glob.glob("/dev/rfcomm*")
+
+	additionalPorts = settings().get(["serial", "additionalPorts"])
+	for additional in additionalPorts:
+		baselist += glob.glob(additional)
+
 	prev = settings().get(["serial", "port"])
 	if prev in baselist:
 		baselist.remove(prev)