reactingFoam: Added run-time selectable LTS support replacing LTSReactingFoam

Select LTS via the ddtScheme:

    ddtSchemes
    {
        default         localEuler rDeltaT;
    }

tutorials/combustion/reactingFoam/ras/counterFlowFlame2DLTS/system/controlDict

@@ -15,7 +15,7 @@ FoamFile
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-application     LTSReactingFoam;
+application     reactingFoam;
 
 startFrom       startTime;