Showing different icon for class and struct in classview

Adding new slightly different icon for Struct to make it
different from Class.

Task-number: QTCREATORBUG-8574
Change-Id: I3da655adeaa05d7a590d4ec00f9749b5d86e0340
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>

src/libs/cplusplus/cplusplus.qbs

@@ -132,6 +132,7 @@ QtcLibrary {
         prefix: "images/"
         files: [
             "class.png",
+            "struct.png",
             "enum.png",
             "enumerator.png",
             "func.png",