Add alternate solarized dark theme.
I've added a Solarized Dark Alternate theme that I think cleans up a few of the issues the current Solarized Dark theme has. I based most of my changes on the Usage Guidelines.
I modified the foreground colors. This is slightly lower contrast, but part of Solarized's design. The current theme actually uses the background from Solarized Light instead of the proper base colors.
I created a new secondary background color to ensure borders and scrollbars still show up properly.