Add Korean localization and Korean 2-set keyboard layout

[hisacat]

First of all, thank you for creating such a great program.

This PR adds the following changes for Korean users:

• Korean translation file
• Korean 2-set keyboard layout

Please review and merge if it looks good.
I hope this project continues to be helpful to even more users in the future 😄

[elvissteinjr]

I can't see anything wrong with this, so no reason to not just straight up merge this.
I'll assume the keyboard works fine and as expected on Korean systems since I can't really judge this. But you wouldn't have done this without reason so, yeah.

Thank you for your help!

[hisacat]

Yep!
just to give a brief explanation:

On a standard Korean keyboard, the "한/영 key" (0x15: VK_KANA/VK_HANGUL) is used to switch between Korean and English input modes.
Since there is no direct way to access the currently selected IME state or input mode, I simply adopted the layout of a typical Korean physical keyboard

Thanks again! 😄