Style-related codepush things

[momijizukamori]

Some quick changes for styles this code push!

Practicality and Bases were the only two layouts that didn't have variables specific to the header navigation links. We've added them, and set them up in all the official layouts, but people who've customized their layouts may want to change those colors.

In Bases:

• Header link background color used to be the module title background color
• Header link border color used to be the module background color
• Header link background color on hover used to be the module link hover color

In Practicality:

• Header link color used to be the header title color

And then we discovered an issue in Planet Caravan where that tag text had no color set, so it was inheriting from the entry text color and creating a situation in a few themes where it was black on a black background. It now has it's own variable, and the offending themes have been fixed.