Document how to regenerate debian/control for other distributions
Removed the embedded copy of libjpeg
Updated the aarch64 port to the version 8u5-b13
Added a description to system-lcms.patch, system-libjpeg.patch and system-libpng.patch
Removed the embedded copies of libpng, libgif and liblcms2
Removed the licenses of lcms, libjpeg, libpng and libgif from debian/copyright
Removed the embedded copy of zlib
Remove generated file debian/control
Create debian/control without preexisting debian/control

Previously, the rule in debian/rules to create debian/control expected
an older debian/control to be present and tried to back it up, which
failed if there was no debian/control. Fix this by only doing the backup
when debian/control exists.