Split "Drupal project" taxonomy term into "Drupal core" and "Drupal.org projects"

See #1057228: Figure out what to document for "Project type" for people doing sandbox collaboration for background.

We should really split up "Drupal.org projects" from "Drupal core" in the project type selector.

Side note: we should remove most of this whole taxonomy and make Project* D7 fieldable and allow different node types for different project types.

However, until that happens (in the Project* 7.x-2.x branch, which will be a while from now most likely) we need to keep working with this taxonomy vocab. It's weird to group Drupal core (something everyone needs) with the issue queue projects for running the *.d.o websites.

In the past, each top-level term in here made the http://drupal.org/project landing page more confusing, but thanks to the redesign, that URL now redirects to http://drupal.org/download which is great, and doesn't automatically show every top-level term in the Project type vocab.

This will make it easier to have a listing of sandbox projects that are clones of core instead of having it all under the weird "Drupal project" term. I think having this split up into two self-documenting terms will also make it less likely that when people create new projects they accidentally pick one of them. Anything hosted on d.o could be considered a "Drupal project", but "Drupal.org project" and "Drupal core" are hopefully going to be more obvious to people creating projects.

Frankly, I think we should add this term and move over core's project ASAP, ideally *before* the Git launch happens and folks start trying to clone core into sandbox projects.

There's no code here, obviously, just a proposal that can be clicked into existence in about 15 seconds once we decide to do it. Hence, needs review. Looking for a rapid RTBC if possible, then I'll pull the trigger. If people see real flaws in the proposal, we can go to needs work.

Thanks,
-Derek