Add wxArtProvider using Tango icons.

The icons are embedded as PNG images directly in the source code to avoid the
need for installing them. This does make the library larger though so provide
a wxUSE_ARTPROVIDER_TANGO option to turn the new code and associated bloat off.
Also turn it off by default under wxGTK as the native art provider is used
there anyhow.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66505 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/artprov.h

@@ -203,6 +203,10 @@ protected:
     friend class wxArtProviderModule;
     // Initializes default provider
     static void InitStdProvider();
+    // Initializes Tango-based icon provider
+#if wxUSE_ARTPROVIDER_TANGO
+    static void InitTangoProvider();
+#endif // wxUSE_ARTPROVIDER_TANGO
     // Initializes platform's native provider, if available (e.g. GTK2)
     static void InitNativeProvider();
     // Destroy caches & all providers