cad/netgen: Update to 6.2.2501 and improve.

• Actualise LICENSE to LGPL21 as in upstream
• Add patches to build with JPEG and MPEG
• Add WWW for source code repository
• Mark i386 as unsupported, as in upstream
• Replace explicit include dirs with localbase:ldflags
• Lint Makefile, sort entries for portclippy(1)
• Replace libav with ffmpeg as a MPEG dependency (see MOVED)
• Strip binaries and shared libraries in post-install phase.
• Change maintainer to alster@vinterdalen.se.

PR: 285491
Reported by: Älven <alster@vinterdalen.se>