First Shader Pass

Pretty hefty update to the client, added shaders from godotshaders.com, specifically:

https://godotshaders.com/shader/hex/ and https://godotshaders.com/shader/pixelated-hex-background/ by grimbeef

https://godotshaders.com/shader/scary-dark-vignette/ by silver637

and the amazing https://godotshaders.com/shader/rtx-filter-for-your-game-brightness-ripples-and-... 

by WhyNilliana

This update does not represent my idea of the final state for shaders, and lacks features like the ability to turn the shaders off. In general though, I think this is a big upgrade for the visuals of the game and moves it much closer to achieving the aesthetic it aims for.