Make this module compatible with Group 2.x as well

Here is a patch to support both versions.

The requirement in the info file also makes it impossible to use:
dependencies:
- group:gnode (>=3.2.0)

I am not sure why that has been added but it seems to restrictive. Version 2 is still supported by group.

New patch removing the hard requirement in the info file.

But the legitimate question is should we have 2 different branches like the Group module?

That's the patch for the beta1 if people need it since the release add some lines at the bottom of the info file that are not in the repo.

That's the patch for the beta1 if people need it since the release add some lines at the bottom of the info file that are not in the repo.

Thank you @phjou for your patches, I will check it and let you know.

I reviewed the patch group-notify-beta1-3436167.patch. I think can go to RTBC.