Various display improvements

To make the reader handier, here are some display improvements:

- a sober, but colorful theme (including a cheap logo)
- masking for email addresses in the body and headers of articles: merely to avoid a few spam…
- displaying of some useful headers (From, Subject, Date): very useful when there is no signature!
- coloration for articles (quotes, signatures, headers), making it easier to read conversations thanks to a fixed color code

I may also add threading one day, with a GMail-like conversation view… But this might make the reader really bloated, though.

Hoping you won’t reject this branch because of the theme change. ;-)