Various changes related to a 0.18 port.

[cfcohen]

I've committed most of these changes separately in case you want to keep some and ignore others. (perhaps the arbitrary enum names?). In conjunction with a matching pull-request on PythonOCC-generator, I was able to build PythonOCC 0.18.

[jf---]

wow, that's great news @cfcohen, did it pass the test suite / could you report on that status if not the case?

[tpaviot]

@cfcohen I cherry-picked all your commits but the last one (arbitrary names for enum). If ever the later is required, we can include it in the conda receipe as a patch