Rewrite statusled implementation.

- Read it now from app.config JSON file.
- Allow for inverted status leds (Sonoff et al)
- Clean up unit tests.

unittest/testdata/testconfig0.json

@@ -1,6 +1,7 @@
 {
-  "name": "3 Gang",
-  "status_led": 0,
+  "name": "3 Gang, inverted statusled",
+  "statusled": 9,
+  "statusled_invert": true,
   "channels": [
     { "led": 2,  "relay": 15, "button": 5  },
     { "led": 14, "relay": 4,  "button": 3  },

unittest/testdata/testconfig1.json

@@ -1,6 +1,6 @@
 {
   "name": "3 Gang, No LEDs",
-  "status_led": -1,
+  "statusled": -1,
   "channels": [
     { "led": -1, "relay": 15, "button": 5  },
     { "led": -1, "relay": 4,  "button": 3  },