science/vmd: update to 1.9.3

• update MASTER_SITES to use upstream stride (the old - repackages - sources were no longer working).
• take maintainership: although I don't use the software I am happy to respond to PR's and check for updates periodically,
• add license information for each source:
  • vmd: custom license that requires the user to explicitly download (and accept the license before downloading). Mark the license as auto-accept here as the present of the DISTFILE will indicate that the license has been accepted
  • tachyon: standard 3-clause BSD license :-)
  • stride: almost BSD license, except only for academic use (i.e. non-commersial) and a requirement to report bugs to the author. Add a plain text copy of the license file to the port.
  • add missing dependencies: gl, x11
  • fix detection of python.
  • simplify configure patch.
  • update pkg-plist for changes in plugin versions.