Add Background Timer Example

Implement a simple apps that use Katzer’s background mode plugin. I
used vibration plugin to vibrate the device after 10 seconds.

Dialogs plugin doesn’t work in background, FYI.

Vibration Plugin:
https://github.com/apache/cordova-plugin-vibration

Background mode plugin:
https://github.com/katzer/cordova-plugin-background-mode

Husa’s Timer.js:
https://github.com/husa/timer.js/