Call dispose() on Components before XWiki shutdown to cleanup resources

The org.xwiki.component.phase.Initializable interface works great to initialize Components.

However, components aren't currently given a chance to clean up resources before XWiki shutdown.

It would make sense to call the org.xwiki.component.phase.Disposable dispose() method on components before shutdown.
This would give components a chance to "properly clean up its resources" per the Disposable javadoc.

This could be used by a temporary file component to delete any outstanding files before XWiki shuts down,
or clean up database connections etc.