Dynamic platform accessories

Complete refactor to homebridge-zp, based on homebridge-lib to use the dynamic platform accessory model.  See #1.

Should also fix #81.

Still work in progress.  Todo:
- Handle topology changes (e.g. create/split stereo pair);
- Handle changed alarms (e.g. move to different zone);
- Hanlde changed config.json (e.g. no longer expose LEDs).
- Handle heartbeat 0 for LEDs to disable polling and use getter.

Need improvements to homebridge-lib:
- Startup sequence seems stable, but feels wrong.  Probably should do synchronous creation of delegates vs asynchronous initialisation.
- Remove accessory, service, characteristic when no longer needed.
- Still issue with name change - simply remove/re-create?
- Double-check tr/catch for every async call.

index.js

@@ -5,10 +5,9 @@
 
 'use strict'
 
-const ZpPlatformModule = require('./lib/ZpPlatform')
-const ZpPlatform = ZpPlatformModule.ZpPlatform
+const ZpPlatform = require('./lib/ZpPlatform')
+const packageJson = require('./package.json')
 
 module.exports = (homebridge) => {
-  ZpPlatformModule.setHomebridge(homebridge)
-  homebridge.registerPlatform('homebridge-zp', 'ZP', ZpPlatform)
+  ZpPlatform.loadPlatform(homebridge, packageJson, 'ZP', ZpPlatform)
 }