dynamically update photos of slideshow

[enopeus]

when a slideshow is started with photoswipe and user adds photos in the album, they are not taken into account.
The best solution would be that they are taken at the end of the current loop, but maybe easyer to do would be to reload the photos taken into account by the diaporam when looping (thus taken into account at the next turn). By the way, the standard diaporama of Piwigo do the job. but it is not as nice as bootstrap photoswipe for other reasons :-)
This will let us use Piwigo in events to display photos in live from people on a screen.