ScriptInfo: report headless if headless attr set

The ModuleInfo interface does not have a dedicated headless setting
(accessor/mutator). So let's use the "headless" attribute by convention.

Author: ctrueden

src/main/java/org/scijava/script/ScriptInfo.java

@@ -332,6 +332,11 @@ public ScriptModule createModule() throws ModuleException {
 		return new ScriptModule(this);
 	}
 
+	@Override
+	public boolean canRunHeadless() {
+		return is("headless");
+	}
+
 	// -- Contextual methods --
 
 	@Override