Addition of the module info structure to allow module information to
be extracted from the modules.

This gives a way to verify the API that the module provides as well
as the version of that API. The hope is that this will make it possible
for MaxScale to detect out of date plugins and either adapt to use them
or reject loading them.

Also added the ability to set a release state on a per module basis.
This allows for production ready and non-production ready plugins to
be identified.