Work with 0.8.2 meteor auth

Features of this PR:

- Make phonegap-oauth work with Meteor `>= v0.8.2` while maintaining support for the `browser-policy` package, details below.
- Close the InAppBrowser when the auth flow is cancelled by the user.
- Close the InAppBrowser on the `exit` event. This is triggered if the back button is pressed and there is no history (right after it is opened).
- Wait until InAppBrowser is loaded before patching the window. This fixes a bug if the meteor application is loaded before cordova is ready -- this will happen if the app is included on the phone locally.
- A better workaround for the InAppBrowser eventListener callback not firing, which also fixes the bug on Android where Cordova plugin callbacks are not processed until the next message.

To support Meteor's latest oauth I patch [`OAuth._endOfLoginResponse`](https://github.com/meteor/meteor/blob/3dfcb42eac34f40b6611a0a0a780b9210467ccb2/packages/oauth/oauth_server.js#L219) to append the credentialToken and credentialSecret to the url hash -- and use them to call `OAuth._handleCredentialSecret` and `Accounts.oauth.tryLoginAfterPopupClosed`. 

This method works even if the meteor app is using the `browser-policy` package which prevents inline 
scripts from being executed. The [`executeScript`](https://github.com/faceyspacey/meteor-phonegap-oauth/blob/54a89728ac1ad1ff898c9eb53726ffde9e3a8ac7/oauth_patch.js#L46) method used in PR #3  will not work under these restrictions since it uses inline scripts.

This PR will only work with Meteor `>= v0.8.2`, as it relies on `OAuth._endOfLoginResponse`.

More context here https://groups.google.com/forum/#!topic/meteor-core/Ma3XTZk4Kqg

~~If https://github.com/meteor/meteor/pull/2220 is accepted we can get rid of the `OAuth._endOfLoginResponse` patch.~~