artifact-refs model to be shared by all builds and descriptors

This PR provides a common model specifying how artifacts are referenced by all WildFly build tools:

1. All XML descriptors may optionally include a root <artifact-refs/> element, where maven artifact coords (groupId, artifactId, extension, classifier and version) are mapped to an artifact name. Artifact refs provide the ability to specify multiple references to same artifact, for instance with different versions.

2. Other XML elements (feature-pack, copy-artifact, etc) reference artifacts through a single “artifact” name attribute, which either:
  * Must match the name of an artifact in artifact-refs.
  * Provide the maven artifact coords required to identify an artifact, in the format <groupId>:<artifactId>[:<extension>[:<classifier>]]:<version>

3. Maven plugins may optionally complement/override <artifact-refs/>, through the maven project dependencies. Each dependency artifact is mapped to the artifact  name <groupId>:<artifactId>[::<classifier>]. Note that this functionality is only activated if property named "use-maven-project-artifact-resolver” is set. By default, the property is only set for the feature pack build plugin.

4.System properties may be used to override the version of any resolved artifact, but only if the property named "system-property-version-overrides” is set. This functionality should be carefully used, specially when overriding artifacts included in feature packs.

This PR includes all schema changes to support this common model. A wildfly-server-provisioning-common-1_0.xsd is introduced, defining the XML elements shared by all XML descriptors, such as the artifact-refs.

Changes to apply on wfly main and core repos, to support updated schemas:
https://github.com/emmartins/wildfly-core/commit/b9e728a5670eaaf23ab2db177efec80eda0defb3
https://github.com/emmartins/wildfly/commit/67bc9f3b9f942478b69759d3cf53cc19fab5b221