[TIMOB-25025] iOS: Document Provider extension does not work with Titanium SDK 6.0.0

This was raised via Slack by [~jeffbonnes] yesterday. He has an [example project](https://github.com/jeffbonnes/appc-doc-provider-example) that worked in Titanium SDK 5.x and does not work with SDK 6.x anymore. Testing it is pretty time-consuming, since you need three app-id's (main app, file provider extension, document provider extension), three provisioning profiles, one app-group and everything linked together in the tiapp.xml. After all, the app builds successful and the extension is visible on iOS. When trying to open it in the system-app "Files" (iOS 11) / "iCloud Drive" (iOS 10), it would then just show a loader and throw the attached error message. We should investigate what changes regarding extensions in SDK 6.0 and fix it in the 6.2.0 time-frame. *EDIT*: There seems to be a general issue with Document Provider extensions on iOS 9 (see [here](http://feedback.textasticapp.com/topics/1723-error-document-picker-both-google-drive-and-working-copy/), and [here](https://stackoverflow.com/questions/45304385/the-document-picker-failed-to-launch)), but as Jeff said, it seems to be working with a native project.