Bug #4234: Use the Firefox Update Process for TBB.

New configure options:
  --with-tor-browser-version=VERSION   # Pass TBB version throughout build.
  --enable-tor-browser-update          # Enable bundle update behavior.
The following files are never updated:
  TorBrowser/Data/Browser/profiles.ini
  TorBrowser/Data/Browser/profile.default/bookmarks.html
  TorBrowser/Data/Tor/torrc