Provides the edit helper and edit helper advice for the Element Type framework.
Edit helpers act as command-factories generating commands to edit a specific kind of model element. Edit helper advice contributes commands 'before' or 'after' the base editing commands contributed by the edit helper.
Clients should subclass org.eclipse.gmf.runtime.emf.type.core.edithelper.AbstractEditHelper
when they wish to implement custom edit helper behaviour. Clients should
subclass org.eclipse.gmf.runtime.emf.type.core.edithelper.AbstractEditHelperAdvice
when they wish to implement custom edit helper advice.