Overall visual theme for ShinySDR

[kpreid]

Right now the main app UI has a particular gray (or very-dark-gray if you change theme) look, and all the other pages (/, manual, tools, site) have plain nearly-unstyled black-on-white.

Some things that could be added:

• [ ] A consistent set of color choices, which ties together the (default-theme) UI and the static pages.
  • Should the static pages follow the theme picker?
• [ ] A modest amount of decoration on the static pages.
• [x] A logo/favicon for ShinySDR.

I've thought about this some already, but I don't have any concrete ideas for any of these things.