Move GTK3 wxNO_BORDER handling to wxControl

So wxNO_BORDER works with other controls, such as wxBitmapButton.
Also use GTK prefix on ApplyCssStyle(), and add an overload that
creates the GtkCssProvider.

include/wx/gtk/window.h

@@ -412,7 +412,8 @@ protected:
 #ifdef __WXGTK3__
     // Use the given CSS string for styling the widget. The provider must be
     // allocated, and remains owned, by the caller.
-    void ApplyCssStyle(GtkCssProvider* provider, const char* style);
+    void GTKApplyCssStyle(GtkCssProvider* provider, const char* style);
+    void GTKApplyCssStyle(const char* style);
 #else // GTK+ < 3
     // Called by ApplyWidgetStyle (which is called by SetFont() and
     // SetXXXColour etc to apply style changed to native widgets) to create