Feature: Gallery view for schematics

[TomLewis]

Via #13

A method screen to have a gallery view of schematics from a folder, with thumbnail cache for speed.

Some options for how it could be accessed from a new screen:

• right click a folder creates an option "view schematics as gallery" or when you highlight multiple schematic files then the option is available?
• when already previewing a . schematic, the normal window we see now, have a button that says "see folder as gallery" with the other buttons, because most schematics are all inside the same folder already!

If it takes a while to process a directory with a lot of large schematics, maybe a background task will need to take over, I have hundreds of schematics I would love to visualize, I have over 11 years of them and as I only have filenames I have no idea whats what now, and there's no easy way for me to visualize them all.

Another option would be to just generate .png thumbnails for each and put those thumbnails into a selected folder, so then no GUI is required to view them all, this then uses the OS gallery view to view these previews of schematics, this would require each screenshot having the correct filename to match the .schematic.

This would have the added benefit of then being able to share these images in say, discord with other players that have access to paste schematics... I think I actually prefer this second method, if we can somehow generate the thumbnails into a folder of choice.