Upgrade to python 3.8?

[capitanevs]

Here I report some (apparently) weird behaviors I caught while writing the code.

In OpticsNumerical

Left is wrong, right is ok

Yellow = rx = ok
grey = sx = wrong

I have no ideas (perhaps try is very strict and it catches warning, too?).

Action: I revert to RX version.

[capitanevs]

LX: wrong
RX: Correct

Screenshot of the error, with LX

Comment:
it must be some stupid "boundary error" (points are 10000, returned are 9999)

In any case, if I geld XProp I should also take care of what is happening to other vectors (which will be made up of \tilde(N) points and not N).

[capitanevs]

We decided that this is not a priority as OASYS is stuck to a previous version of python.

Compativility with Python> 3.7 COULD BE RELEVANT when using LibWiser only, but this is not a priority now.