Fold in pre 3.0 Tor Browser changelogs
We should fold in the pre 3.0 Tor Browser changelogs for reference purposes. They are right here: https://gitweb.torproject.org/torbrowser.git/tree/?h=maint-2.4. Might be a bit of work to sort all the things out and get that into the format we use today, but it's worthwhile.