Integrate Elytron for management security.

This is a top level container task for the integration of Elytron for domain management security.

Do note however that the purpose of Elytron is a single unified security solution across the whole of the application server so many tasks here will be groundwork for the remainder of the integration.

At the moment the Elytron subsystem is being developed outside of wildfly-core, this will need to change in the future due to dependency issues (i.e. to write a subsystem you need to depend on core and core will need to include the subsystem (I think.)). However this will make it easier for now to ensure that the subsystem is 100% with no WildFly code accessing the subsystem - and also verify that we can create a distribtion with out the subsystem and still have a functional server.

Overall if someone came up with an alternative subsystem that provided the same capabilities it should be possible to drop it in.