security/clamtk: Update 6.18 => 6.19, take maintainership, switch upstream, improve port
Changelog:
https://github.com/piposeimandi/clamtk/blob/32cc526/CHANGES
Switch upstream to most active fork.
Improve port, fix warnings from portclippy.
Co-authored-by: Vladimir Druzenko <vvd@FreeBSD.org>