- cmake: remove zintconfig.h.in for now as incompatible with MSVC

project builds (will add back in future if go fully CMake)
- NO_PNG -> ZINT_NO_PNG and new API function `Zint_NoPng()` to
  determine if no PNG support in libzint; replace use in GUI with
  backend_qt method `noPng()`

backend_qt/qzint.cpp

@@ -682,6 +682,10 @@ namespace Zint {
         return m_lastError.length();
     }
 
+    bool QZint::noPng() const {
+        return ZBarcode_NoPng() == 1;
+    }
+
     int QZint::getVersion() const {
         return ZBarcode_Version();
     }