added icons for Xpand/Generic SGen

plugins/org.yakindu.sct.generator.core/plugin.xml

@@ -34,6 +34,7 @@
           contentType="statechart"
           description="Generate Code using Xpand Templates"
           elementRefType="org.yakindu.sct.model.sgraph.Statechart"
+          icon="icons/sct.png"
           id="yakindu::xpand"
           name="Custom Xpand-based Generator">
        <FeatureLibrary
@@ -59,6 +60,7 @@
          contentType="statechart"
          description="Generate Code using Xpand Templates"
          elementRefType="org.yakindu.sct.model.sgraph.Statechart"
+         icon="icons/sct.png"
          id="yakindu::generic"
          name="Custom Xtend2/Java-based Generator">
       <FeatureLibrary