checkInputs used to be added to nativeBuildInputs. Now we have
nativeCheckInputs to do that instead. Doing this treewide change allows
to keep hashes identical to before the introduction of
nativeCheckInputs.
Add an optional withGui flag to turn off gui as most of the time it's
not needed since this is a python library.
Use a GitHub tarball to optionally enable tests, currently disabled by
default, but next release' tests should pass (tested the beta release
tag).
Wrap qt apps properly, without double wrapping, if gui is enabled.
