Many changes

[huanie]

Quite a lot of changes in this pull request. I doubt that I can split it up.

Internal changes

• Move to ListView because it's more efficient.
• ListView and CompactView are in their own files.
• Updated GTK version for newer API and macros.
• Commandline arguments are globally accessible with a OnceCell (move to LazyCell when it hits stable).

Enhancements

• Thumbnails are generated in a multithreaded way. No more lags.
• Memory usage decreased by only storing needed thumbnail size.
• Drag and Drop Area is the entire window.
• Dropping multiple files is now possible
• Window width and height is now correctly applied
• --target can accept multiple files.

New features

• Multiselection. Hold CTRL to select files to drag. Will move to single drag when dragging something that is not selected. (Opening is still single selection)
• Removed window decorations.
• Q and q will also quit the application.
• No more buttons because they do not wrap their text.

[nik012003]

Snap, it looks like the build fails for ubuntu 22.04, since it has an older gtk version. Are we using any new features from >gtk4.6 ? If not, we should use set the 4.6 feature flag in the gtk-rs crate.

[nik012003]

Perfect, will merge as soon as I get home this weekend.