Add Slideshow Support

[JoeGeeGameDev]

It would be a fantastic feature to have "play" for every folder that starts a slideshow per folder (on order or random options) so that i can just give it a couple of seconds to fave the pics I like without clicking, just play and lay back.

[RupertAvery]

If you press Space in the Preview, it will start a slideshow where the next image will be shown every 5 seconds. As for randomized, there is an option to sort by random, which will randomize every page, so it's not perfect.

The delay before moving to the next image can be set via Settings > Images > Slide show delay