doc: Minor consistency updates

[jayschwa]

Minor changes which improve docs.julialang.org's consistency with julialang.org.

[pao]

This probably conflicts with #2123? Also, the fork banner doesn't make any sense on the docs page.

[jayschwa]

I suppose not, but the banner is included on every other section of the site, even pages where it may not make sense (e.g. downloads or blog).

[pao]

Still, a foolish consistency and all that. @nolta should probably be the one to check this all out though.

[jayschwa]

It looks like the addition of DejaVu Serif and favicon are still applicable to @nolta's branch. It might be better if the favicon source is http://julialang.org/favicon.ico so there isn't a duplicate copy, but I wasn't sure how to do that from within the Sphinx config.

[pao]

Looks like the <link rel="shortcut icon"...> bit is in the basic layout template that the Julia theme extends: https://bitbucket.org/birkenfeld/sphinx/src/tip/sphinx/themes/basic/layout.html

[nolta]

Thanks Jay! I cherry picked the first two commits, and vetoed the fork patch. The favicon patch is fine, but i'd rather we store the file somewhere else.