update the Coin3D stack to it's latest release

Coin has moved to a new place on the web https://coin3d.github.io/
and the project has rolled new releases. Additionally, it's undergoing
relicensing (most parts are now licensed user BSD 3-clause).

This updates

graphics/Coin to 4.0
graphics/py-pivy to 0.6.5
x11-toolkits/soqt to 1.6.0

Further, graphics/py-pivy-devel and x11-toolkits/soqt-devel have been
renamed to graphics/py-pivy and x11-toolkits/soqt respectively (losing
their -devel suffixes). Previously, these ports had been forks and/or
pre-releases of the old Qt4-based pivy and soqt ports. As these old ports
are long gone and these new versions have been updated to officially
released versions, it seemed prudent to remove the devel from their names.

Bumping FreeCAD for dependency change.
Adding PORTEPOCH to soqt to prevent PKGVERSION going backwards.

Thanks to pfg@, who contributed the update to graphics/Coin and reviewed
my patches.

While here, I'm taking over maintainership of these ports.

Submitted by: pfg@ (graphics/Coin)
Reviewed by: pfg@