Update Tor Browser spec for 10.0
Tor Browser 7.5 is out. We should update our design document to cover all the new issues that are showing up in it. Highlights are
- Switch to rbm/tor-browser-build
- The security slider copy update ...
Additionally, we should fold in all the 8.0, 8.5, 9.0, 9.5, and 10.0 changes.