Fix Cython installation for fresh CPythons
We try to fetch a wheel only and if that fails, we disable compilation.
Useful for fresh CPythons such as 3.8 now, where wheels are not yet ready,
but Cython defaults to compiling (because it detects CPython).
Note that --install-option="--no-cython-compile" makes pip use source package,
hence we don't want to use it right away. We still prefer wheel over