Add online and offiline plugin-network-information events support for the Browser platform

Initial implementation used XHR to check whether we connected to network or not. Two main problems of this approach is that it used CORS and wasn't able to detect local network access.
So for better compatibility with specs it is better to use browsers native implementation of navigator.onLine property which properly handles all the aspects of network accessibility.
navigator.onLine available for all modern browsers: http://caniuse.com/#feat=online-status