Change shadow for "Follow logs" button

In general, the "light" on web pages come from directly above, so
shadows should be directly below things. This isn't really a shadow,
though, but rather a way to make it seem like the text is "embossed"
into the surface by giving it a slight sheen on the bottom edge, in
which case the shadow definitely shouldn't be shifted left or right.
Download 2x images from Gravatar

This will make them look nicer on Retina screens. We may want to make
them even bigger if people are increasing the size of the page on
Travis, but doing that causes all kinds of alignment issues, so it's not
necessary to do now, I think.
Add newsletter link to "Community" menu.