New: graphics/scantailor-advanced: Interactive post-processing of scanned pages

scantailor-advanced is an interactive/GUI post-processing program for 
scanned pages (jpg|png|tiff, not pnm) offering de-skew, crop, rotation, 
'binarisation', de-speckle, de-warp, etc.

Based on a currently-maintained fork of previous projects 
scantailor/scantailor-enhanced. I have kept the rather long name 
scantailor-advanced to differentiate from these and match the binary 
filename.

Built against Qt6 (Qt5 is also possible/tested, but Qt5 HiDPI support is 
basic).

There is a website https://scantailor.net that hints it is the 
'official' one: actually it links to a fork that is behind the active 
project and offers little except marketing claims, so I have not added 
it as HOMEPAGE.

tested on amd64/current (Aug 14) and amd64/7.9-stable with a few 
mono/greyscale document scans.

Tests/comments welcome. Is this of interest to import if OK?

Chris