Prepare tor-browser-build for building stable releases
Up to now we used
tor-browser-build to only build alpha and nightly bundles but we think it is mature enough to fully replace Gitian.
This bug tracks the changes we need to make to be able to build stable, alpha, and nightly bundles from the same branch.
If we think that gets too messy we move back to make dedicated
maint-XX branches. We'd like to avoid that, though, as it has been confusing in the past for users that wanted to build Tor Browser.