Have Tails Installer in Jessie backports

Originally created by @sajolida on #8805 (Redmine)

The installer will be ready around 6 months after the release of Jessie. It makes a lot of sense to have it backported quite soon.

This is not officially blocking tails/fundraising#8538, but maybe it should is possible.

Edited May 15, 2020 by sajolida

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