Make a policy for deprecating IOs

[zm711]

KwikIO for the Kwik format of stuff constantly throws warnings (I believe it is meant for python < 3.7). We should have a policy for either removing from tests or removing from the code base if something is unsupportable. Some of these warnings will become hard errors soon.

If we remove from tests we warn the user that it requires old versions of python that must be installed etc at the users own risk

If we remove the io completely maybe have a warning that says this io has been removed and if needed the user should use an old version of neo?

[zm711]

Policy discussed was that:

1. Removal of IO once there are no versions of python/numpy which can support the IO + add class with warning explaining to downgrade to an earlier version of Neo
2. add warning to IO if the python/numpy version is limited to let the user know they need to pick a different version

[h-mayorquin]

This makes sense. I will also ease development burden.