cordova-plugin-inappbrowser support for custom URL schemes, as needed for oAuth

A very common usage of the inappbrowser is to open a URL to the apps server, as part of the oAuth flow.  After a secure token is created, the final step in the oAuth flow is to redirect back to the Cordova app, to proceed as authenticated.  At the WeVote open source project we use this to authenticate with Twitter and Facebook, other projects want to authenticate with Google, Whatsapp, Skype, etc. 

There is a package for React Native react-native-oauth that does this, and I was able to get oAuth working for iOS with cordova-plugin-safariviewcontroller, but there is nothing that is stable, maintained, and working that is equivalent for Android.

A pull request will follow that uses whitelisted schemes to allow the oAuth redirect to complete through the InAppBrowser.  It is a fairly simple code change, that leads to a simple end user implementation, that should be widely appreciated (based on years of mostly unfulfilled Stack Overflow chatter.)

This PR builds on  https://github.com/apache/cordova-plugin-inappbrowser/pull/99 and https://github.com/apache/cordova-plugin-inappbrowser/pull/261 and builds on a good suggestion from NGumby and comments about viability from infil00p