STYLE: add OpenFOAM icon to Doxygen pages

doc/Doxygen/FoamHeader.html

@@ -7,6 +7,7 @@
 <!-- html,info -->
 <link rel="stylesheet" type="text/css" href="../Doxygen.css">
 <link rel="stylesheet" type="text/css" href="../tabs.css">
+<link href="../OpenFOAMicon.png" type="image/png" rel="icon" />
 <meta name="keywords" content="computational fluid dynamics, CFD, OpenCFD, OpenFOAM, open source CFD, open source">
 <meta name="description" content="OpenCFD Ltd, leaders in open source Computational Fluid Dynamics (CFD), the developers and maintainers of OpenFOAM: the open source CFD toolbox. We supply support and contracted developments for OpenFOAM">
 </head>