External resource overlay

To enable/disable the external resource overlay, simply call:

org.eclipse.emf.facet.infra.browser.uicore.CustomizationManager#setDecorateExternalResources(boolean)

with the overlay	without the overlay

Test scenario

Here is a scenario to check that it works:

• start Eclipse with this plug-in enabled: org.eclipse.emf.facet.infra.browser.uicore.examples.cnf (but org.eclipse.gmt.modisco.infra.browser.uicore.examples.cnf disabled)
• open the Project Explorer view
• expand a .ecore file, and see that the EFactory element(s) under the EPackage#eFactoryInstance reference have a blue arrow
• now, add the following code at the end of the method org.eclipse.emf.facet.infra.browser.uicore.examples.cnf.Activator#init:

customizationManager.setDecorateExternalResources(false);

• restart the runtime Eclipse
• check that the EFactory element(s) under the EPackage#eFactoryInstance don't have a blue arrow anymore