create 10.8 branch

create 10.8 branch:

• git checkout origin/10.7 -b 10.8 --no-track
• change VERSION (10.8.0-alpha)
• rename and change files in debian/
  • find debian -name '*10.7*'
  • grep -r 10.7 debian
  • it's almost always s/10.7/10.8/ except in debian/control in Breaks/Replaces lists.
• buildbot config
  • same, search for 10.7, replace with 10.8 or add 10.8 to the list, as needed
• git push origin HEAD:bb-10.8-release
• verify in buildbot that everything works
• git push --set-upstream origin HEAD:10.8
• change the default branch on github, enable branch protection