Added 4 themes by Scout339

[Scout339]

More themes!

• I understand and have followed the contribution guide
• I have tested my changes locally and they are working as intended

Hello! first time forking and making a pull, hopefully I didn't do too much as an inexperience GIT user. Attempted to follow the contribution guidelines and built the themes on my personal machine before trying to learn the basics of Github to officially add some of my themes to the repo!

• Dark Signal is the only one that I used some CSS for just to see what I could do with some limited knowledge, but is based off of the Signal Desktop app's official dark theme.
• Paperwhite is a port of my Discord Light Theme 2.0 Concept (that actually was the inspiration for Discord to remake their Light Theme as it is now marked 'completed' on their forums! https://support.discord.com/hc/en-us/community/posts/360043415712-A-concept-to-improve-Discord-s-light-Theme)
• Sonar was originally the start of Dark Signal, but I accidentally made something different and leaned into the difference in colors to end up making an entirely different theme.
• Steamy is as close as I could get to porting the Steam Desktop App's color theme, and it ended up looking nice, so why not include it?

[DeclanChidlow]

Congrats on your first PR!

The theme folder names should be lowercase rather then uppercase as seen in the other themes, but it otherwise looks good.

Please fix that and I'll merge it.

[Scout339]

Alright, I'm pretty sure I made the changes correctly. Strange that it mentions deleting something that was never merged to the original project as a change to merge, but the syntax for the themes should be correct!

[DeclanChidlow]

Git and GitHub copy can be a tad unintuitive, but all your changes were good to go.

Your themes should be appearing on Discover shortly. :)