Nodeaccess limited to a single role

For my use case I needed specific functionality to allow granting permissions for just a single role. Every other role would be untouched by nodeaccess.

So user with this new specific role can be granted the edit permission to edit certain pages, without allowing them anything else.

I've made quite a few modifications to this module to make it work. Some of the added functionality might be of use for other people. Therefore I'm throwing my patch here. But as a whole it might not (yet) be suitable for inclusion in the module.

I'll put the patch and a changelog in the first comment below.

Remaining tasks

If there's a desire from the wider community of users of nodeaccess to add any or all functionality to the module, remaining tasks -- in no particular order / either of these could happen first:

• Discuss and decide which pieces to add to module.
• Break out pieces into child issues.