Hg 249

@hakubo @kenkouot @aquilax @mklucsarits @nandy-andy @rogatty 

This makes the gallery hop to the next / prev media on tap on an unzoomed gallery item. Works only for images, as tap on a video usually means that user wants to watch it, not jump to another one ;)
`viewportSize` can change, right? Should there be `.property('viewportSize')`?