Add an intermediate "dark" background color option

[b16r05]

I have been on flym for so long, because I love the colors.

spaRSS background dark is actually BLACK. Flym dark background has more white making it GREY. Consider adding an intermediate color option to sparRSS. When in low brightness, READ items are almost invisible because of the background.

Further, adding texture would be even better. Github itself has a cool dark textured theme: https://userstyles.org/styles/37035/github-dark Github page: https://github.com/StylishThemes/Github-Dark says "Your eyes will ❤️ you." -- : )

[b16r05]

I looked at replacing spaRSS "colors.xml" with Flym's "colors.xml" but they are different... I don't think this will work. SpaRSS "color.xml" is complicated.

https://github.com/Etuldan/spaRSS/blob/master/mobile/src/main/res/values/colors.xml https://github.com/FredJul/Flym/blob/master/Flym/src/main/res/values/colors.xml