Decouple rendering of UI from internal state (such as images held)

[gurgalex]

I think this would make writing tests easier, as the internal state of the application (ex. current image index) could be tested before and after without needing to spawn an sdl2 window.

[Davejkane]

Yeah, I'm already starting to get a little weary of the Program god struct. Is this something you'd like to take a look at? If you have something in particular in mind?

[gurgalex]

Yeah, I'd like to take a look at it.

Seperating images, dest_folder, index from the UI is a start.

Communicating data changes to and from the UI / data source

Example data structure and communication. I'll see how it goes.
see fn update_counter
https://azul.rs/

I'm sure there are other ways to go about making testing / splitting up easier.

[Davejkane]

I'm taking care of this in the info bar branch.