STYLE: engineFoam: Renamed engineFoam -> XiEngineFoam and sprayEngineFoam -> engineFoam

XiEngineFoam is a premixed/partially-premixed combustion engine solver which
exclusively uses the Xi flamelet combustion model.

engineFoam is a general engine solver for inhomogeneous combustion with or
without spray supporting run-time selection of the chemistry-based combustion
model.

tutorials/combustion/XiEngineFoam/kivaTest/otape17

@@ -1,4 +1,4 @@
- K3PREP/100198 4-valve pentroof engine (082096/1135), 052899/1030               
+ K3PREP/100198 4-valve pentroof engine (082096/1135), 052899/1030
 35023 52043 3
 1 0 0 0 0 -1
 2 0 0 0 0 -1

tutorials/combustion/XiEngineFoam/kivaTest/system/controlDict

@@ -15,7 +15,7 @@ FoamFile
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-application     engineFoam;
+application     XiEngineFoam;
 
 startFrom       startTime;