Feature turbulence

Turbulence updates from our internal development line:

• Added DESModel base class for DES models
• Moved DES models to separate DES directory
• Added DESModelRegions function object
• Updated porousBafflePressure BC to use DataEntry class for D and I inputs
• Documentation updates

src/TurbulenceModels/turbulenceModels/DES/DESModel/DESModelDoc.H

+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2015 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+\defgroup grpDESTurbulence DES
+@{
+    \ingroup grpTurbulence
+    This group contains DES turbulence models.
+@}
+
+\*---------------------------------------------------------------------------*/