Wrap initialization logic for iOS into a conditionally loaded module

[aoberoi]

Currently the project requires an application developer to use a bit of code (only for iOS) so that the JS is executed in the right order.

if (window.device.platform === 'iOS') {
   cordova.plugins.iosrtc.registerGlobals();
   window.OT = cordova.require('cordova-plugin-opentokjs.OpenTokClient');
 }

This is brittle and we might be able to hide this implementation detail inside a conditionally loaded only for the iOS platform. That would take away the dependency on cordova-plugin-device.

Additionally, other iOS specific manipulations of the opentok.js library could be handled in this script.

[aoberoi]

• the refreshVideos() method might be able to be mounted into the OT namespace, and called automatically in certain instances.
• the OT.setLogLevel() method could be enhanced by adding logging for iosrtc as well.