Solution to commons-ios-test

Completed the following:

Core exercises:

1) Detect login and upload errors and give feedback to the user.
2) After uploading, display a button that opens the new file in Safari;
use URL format 'http://test.wikipedia.org/wiki/File:' + filename
3) Move i/o off the UI thread and provide visual progress feedback.

Bonus exercises:

Use correct naming style for UI field properties in controller classes.

When pulling existing images from the gallery, retrieve the original
file via asset URL and upload that instead of recompression from a
UIImage