add fullscreen mode

[cgahr]

Hi,

I'd love to have a fullscreen mode for rmview.

I use rmView to present my slides via my laptop using the remarkable. The nice thing is that I can take notes or explain things directly using the pen.

However, I cannot put rmview into fullscreen, which wastes a bit of space on the bottom and top of the screen.

BR, cgahr

PS: really love rmview!