Tails Installer should display accurate progress information instead for freezing on "Synchronizing data on disk..."

During test sessions, Tails Installer was stucking a long moment at 95%.
I don’t kown if it’s happening often. Any feedback ?

If it’s often stucking, could we have an other way to indicate the progression ?

Feature Branch: feature/gtk3+fancy-progress-bar

Original created by @tchou on 10114 (Redmine)

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