Remove links to planets other than Planet Outreach
Remove the "Create a planet" section on the front page.

We don't really want to allow arbitrary planet hosting at the moment - the
main goal is to host Planet Outreach. While not entirely disabling the
Planet creation code, we make it hard to reach by removing the form from
the front page.
Remove donate links from navbar and blog info page

Planeteria is not currently hosted by James Vasile, so it doesn't
make sense to have his donation information linked.
Fix link to jQuery

JQuery wasn't getting loaded because the link to the JS file was wrong.
navbar.html: Temporarily unlink about.html

about.html has a lot of out-of-date information about planeteria.info; until
we figure out exactly how we are handling this site (do we strip it down to
just Planet Outreach and remove all planeteria content?) unlink about.htmt
from the header to not be confusing. We still link it from the footer since
there is some important legal information there.
Fix links to code on github

Link to owtaylor/Planeteria rather than jvasile/Planeteria, since we should
link the code that is actually running on the site.