[Fedora-spins] Spin-kickstarts branching

The schedule has today as the day we create an F15 branch of spin-kickstarts. Barring any objections I'll do this tonight. Once it's done I'll send another notice. After the branch, I'll change master to point to the rawhide repos. I'll make a new spin-kickstarts package update. And the nightlies should starting using the F15 branch until a bit after the release.