reactingEulerFoam::functionObjects::phaseMap: New functionObject to write the phase map field

Description
    This functionObject writes the phase-fraction map field alpha.map with
    incremental value ranges for each phase
    e.g., with values 0-1 for water, 1-2 for air, 2-3 for oil etc.

    Example of function object specification:
    \verbatim
    phaseMap
    {
        type            phaseMap;
        libs            ("libreactingEulerFoamFunctionObjects.so");
        writeControl    writeTime;
    }
    \endverbatim

Usage
    \table
        Property     | Description             | Required    | Default value
        type         | type name: phaseMap     | yes         |
    \endtable

This replaces the alphas functionality previously built-in to
reactingMultiphaseEulerFoam so that the storage, calculation and writing of the
phase map field is now under user control.

tutorials/multiphase/reactingMultiphaseEulerFoam/laminar/mixerVessel2D/system/controlDict

@@ -51,5 +51,9 @@ maxCo           0.5;
 
 maxDeltaT       1;
 
+functions
+{
+    #includeFunc phaseMap
+}
 
 // ************************************************************************* //