[evince] Feature request: Invert background color too

[Sandro Kalbermatter <sandroka student ethz ch>]

Hi there!
I absolutely love evince. However, there's something that I think is 
missing: When looking at a white document and the eyes start to hurt, 
Ctrl+i does great work protecting the eyes by inverting the colors. 
Unfortunately, the background color is not inverted, so everything 
surrounding the page now seems way too bright.
I think it'd be great if the background turned black when inverting the 
PDF's colors. Then, the user can get rid of the menu bar by pressing F11 
and the entire screen is nicely dark (except for the text), relaxing the 
user's eyes.
Statistically, this behaviour makes sence, because the very most PDFs 
that people spend a long time on have white background that turns black 
when inverting the colors. Therefore, the evince background (margins 
left and right, and the space between the pages) should turn black also 
when in inverted mode.
Thanks for this great program!
Sandro