Add cat images to demo app. CC licened from Flickr:
https://www.flickr.com/photos/aigle_dore/6672148713
https://www.flickr.com/photos/missblythe/1484248550
https://www.flickr.com/photos/54844390@N05/5110834170
https://www.flickr.com/photos/chaukar/9806556103
New screenshot
Merge pull request #59 from cbowns/develop

Add a less offensive app screenshot