* control changes
* fix truncating sets names
* unify stretch and focal code

szarp-python3-transition is temporary dependency, Ubuntu Focal Fossa
(and incoming Debian Bullseye) has no support for python2 packages and
SZARP for previous distributions is not ready for python3 usage. SZARP
will be continuously ported to python3 and python2 dependencies should
be removed soon (as well as szarp-python3-transition package). Buster
has support for both python2 and python3 packages but it has conflict
with libcgal-dev (Focal Fossa too). Relationship between libcgal-dev
and szarp-python3-transition package allows to build SZARP on buster
(build without CGAL is allowed but removes XYZ graphs functionality).