A number of minor styling/front-end fixes
Fixes for a number of minor styling or front-end issues. Each fix is in a separate commit, so it should be simple to pick a subset if needed.
- Add ids to settings headings to allow links to sub-sections (#638 (closed))
- Apply proper styling to comments that are both new and by OP (#371 (closed))
- Keep dropdown menu visible when using keyboard navigation (part of #747)
- Fix theme preview colors for the Zenburn theme
- Fix visited link coloring hiding subscribed status in groups list (#720 (closed))
- Fix striped table backgrounds within blockquotes (#659 (closed))
I'm still working on getting the dev environment set up, so I haven't been able to run complete tests, but I'm pretty confident that they all work, and I've manually tested the CSS changes.