Do not in-place upgrade to TBB v8 (ESR60)

TBB updater shouldn't upgrade current TBB 7.x users. Instead, show a dialogue:

=== A new TBB is now available! Please download new TBB from https://tpo

Everyone should start using fresh browser - ESR52 and 60 is completely different.

If you use updater to do in-place upgrade, many people will carry over old settings and some might cause a persistent problem.