'j/k' key bindings for 'next'/'prev' slide
Dont display photo container until we have photos
Make things work on small screens

Switch from using width and height to max-width and max-height but set
`.photos` width to 100% so that it can render.
recalculate the slider in 'resize' window handler
There are some issues with margin still slider is rendered on a small
screen
Add prev and next buttons to the photo