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

Add USES=xorg USES=gl, ports categories x

Add USES=xorg and USES=gl to ports in categories starting with 'x'
While here, try to sprinkle other USES (mostly gnome and sdl) as needed.

Bump PORTREVISION for ports depending on the canonical version of GCC
as defined in Mk/bsd.default-versions.mk which has moved from GCC 8.3
to GCC 9.1 under most circumstances now after revision 507371.

This includes ports
 - with USE_GCC=yes or USE_GCC=any,
 - with USES=fortran,
 - using Mk/bsd.octave.mk which in turn features USES=fortran, and
 - with USES=compiler specifying openmp, nestedfct, c11, c++0x, c++11-lang,
   c++11-lib, c++14-lang, c++17-lang, or gcc-c++11-lib
plus, everything INDEX-11 shows with a dependency on lang/gcc9 now.

PR:		238330

soqt-devel: fix build with GCC-based architectures

and add localbase:ldflags to simplify CPPFLAGS/LDFLAGS

PR:		235659
Submitted by:	Piotr Kubaj

Add soqt-devel, which is a forked and updated version of soqt

This fork has been prepared by the FreeCAD project, to support Qt5