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/Icons.h

@@ -51,6 +51,7 @@ public:
 
     enum IconType {
         ClassIconType = 0,
+        StructIconType,
         EnumIconType,
         EnumeratorIconType,
         FuncPublicIconType,
@@ -74,6 +75,7 @@ public:
 
 private:
     QIcon _classIcon;
+    QIcon _structIcon;
     QIcon _enumIcon;
     QIcon _enumeratorIcon;
     QIcon _funcPublicIcon;