Drop support for polymake before version 4, and switch to "native" JSON file format support

[fingolfin]

With help of the JSON GAP package it would be possible to fully parse the files produce by polymake, instead of hacking things together. That would make it possible to e.g. fully support HASSE_DIAGRAM again. A lot of special casing could perhaps also go away.

And by generating version 4 files, one would avoid the pesky warnings

polymake: upgrading /tmp/gaptempdiryNGNZ7/tmpIn.log from old plain file format