Add Ubuntu theme
I used to have a mockup of this theme made using browser devtools, but I lost it. Whoops.
There are only 4 themes: white, black, paperish, and dark blue. There isn't much variance. However, the Ubuntu theme has this variance: orange for the background, white for the body background, gray for text, and purple for interactive content. Color codes for Ubuntu are sourced from here Maybe we could have this theme in Tildes?