[AS7-6551] Add version 2.0 of jboss-as-config schema.

Also update existing configuration based on 1.4 to use 2.0.

Whilst normally it would be desirable for this change to go in with the same change that actually causes the need for a new schema version at the moment we have a few pull requests in the queue that need porting to version 2.0 of the schema so this pull request is to provide a common base.

Additionally by being in it's own commit we can see what changes are actually made to the 2.0 schema.