Re-introduce the BookletImposer PDF imposition toolkit

i.e. revert 56c81e5eccf893a4cafccbb63ce1924c7a5cec52 since the bookletimposer situation was fixed and it’s back in Stretch.

Feature Branch: feature/12686-reintroduce-bookletimposer

Original created by @intrigeri on 12686 (Redmine)

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