Fix help menu which currently tries to open help files from
share/sane/xsane/doc instead of share/doc/xsane where they are
installed.

While here

• Add LICENSE_FILE
• Pet portlint: regenerate and rename patches
• Switch GIMP option to options helpers
• Fix pkg-message. The GIMP plugin now shows up in File->Create and not in File->Acquire.

PR: 218989
Approved by: lme (mentor), koalative@gmail.com (maintainer timeout, 4 weeks)
Differential Revision: https://reviews.freebsd.org/D10752