Left-handed cursor option

[cassidyjames]

As pointed out on Twitter, the default cursor is designed for a right-handedness by default. It might be more inclusive to offer a left-handed (horizontally mirrored) cursor option for left-handedness.

If I understand correctly, this would also require an entire left-handed cursor theme, though it should be relatively easy to mirror some things once? I will open an issue on the icons for that.