Image viewer for uploads + some fixes

I added an image viewer for the uploads that can be accessed by tapping the image preview in the detail view.

A larger version of the image is downloaded and displayed if the upload has already been completed, if the upload is still queued the local file is used.

Also I fixed a minor bug where the *Upload* button would still be enabled even if there were no uploads queued, and I fixed a typo I made in a method declaration in **CommonsApp**, and lastly I fixed something caught by Xcode's static analyzer.