tiling & fixes

Hi,

Apparently the shader was quite broken for some people (horizontal lines & stuff). Those should (hopefully) not appear anymore (or way less at least). Let me know if it's still broken though.

2 new additions:

• Tiling: Enable this to create backgrounds that are seamless and will tile infinitely. I recommend disabling the planets, those might look kinda odd when repeating a lot.
• Darkening: You want a darker space but still have the dust & nebulae? Now you can, this will simply use some more darker colors.

Thank you all for following the project, appreciate it!