Update README and xcconfig to remove the "Integration Tests-Info.plist" setting

Implementation of #144

The existing README images come from the Subliminal website (which is from the gh-pages branch I assume). I added a directory for documentation images to the master branch, since otherwise I would need a second PR to the gh-pages branch. I can make a separate PR to gh-pages if you want to keep all the images on inkling.github.io/Subliminal