Migrate to Tor Browser 6.0.x based on Firefox 45.2

The Tor Browser that will be published at the same time as Tails 2.4 will be version 6.x, based on Firefox 45.2.

Feature Branch: feature/11403-tor-browser-6.x

Original created by @anonym on 11403 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information