Attribute group basics

Basic elements of "attribute group" handling as discussed on the wildfly-dev list in the thread starting at http://lists.jboss.org/pipermail/wildfly-dev/2014-December/003414.html

This JIRA is for the non-CLI aspects of the "Part II Proposed Work" section of that email. The CLI ls -l aspect, as well as items in the "PART III Other possible things to do" section are not included. Separate JIRAs will be filed for such things.

Specifically, this covers:

1) The basics

We add a piece of metadata to the read-resource-description output for
an attribute. Name is 'attribute-group', value type is ModelType.STRING,
value is the name of the group, with 'undefined' allowed.

The group is simply the set of attributes that share the same string.

To implement this, we add public String
AttributeDefinition.getAttributeGroup() and add support for setting it
to the relevant Builder. AttributeDescription.getNoTextDescription outputs the value when it gets called by handlers for read-resource-description and read-operation-description.

2) XML parsing/marshalling

Modify PersistentResourceXMLDescription such that attributes in an
attribute group get persisted in their own child element, whose name is
the name of the group.

PersistentResourceXMLBuilder exposes a setter to allow users to turn
this on/off for that resource. Turning it off will allow the addition of
attribute group settings for a resource without requiring an immediate
corresponding xsd change.

3) Low level management API

The output of read-resource and read-resource-description is modified
such that attributes are sorted by group name and then by attribute name.