design: Fix default link colors

[cwhite911]

The link colors are current set to use the secondary color, but the should use the primary color.

[echoix]

Thanks for filing it in, we noticed it during the summit, and indeed links in the text are very hard to discern

[ecodiv]

Indeed, I was looking for the link to the grass addons, initially overlooking the link on https://grass.osgeo.org/download/addons/ due to the color.

[cwhite911]

Thanks! I have a bunch of updates I'm going to be making now to finish synchronizing the website with the the Docs and tutorials. I was saving the website for last because it is the most complicated.

With that said if you see things that look wrong please add it as a sub issue to the parent of this issue to make sure it's on my radar.