i was afraid for the futur of my galleries. Nextgen i tray several times version after 1,9,13 no, no work at all. And since 3.9 i have to remember shortcode ([slideshow id=35][nggallery id=25] and so on) because not work in the edit.
I was searching again, yet another time for an other plugin for galleries, no success.
And just to day i see yours. But in english, for a french, the resume http://wordpress.org/plugins/tags/gallery is no really understanding…
Well to day i try yours… woooh it works ! thanks i am saving.