How do o add options to the edit gallery page

I have a modified Gallery shortcode wich if presented with [gallery slideshow="true"] will output a slideshow instead of just some columns with thumbnails.

What I would like to achive is not having to type slideshow="true" eveytime i want a slideshow, but having a checkbox in the edit gallery settings panel.

I’ve been scaning trough the codex but cant seem to find anny information on how to add options to the new edit gallery settings panel, and include them in the shortcode.