functionObjects::XiReactionRate: Writes the turbulent flame-speed and reaction-rate volScalarFields for the Xi-based combustion models

Replaces the obsolete and 'wdot' utility.

postProcess -func writeCellCentres

being filled with cellLevel files, which generally breaks workflows

Instead of ICCG use PCG with the DIC preconditioner
Instead of BICCG use PBiCG with the DILU preconditioner

Replaced the 'postProcess' argument to the 'write' and 'execute'
functions with the single static member 'postProcess' in the
functionObject base-class.

e.g.
    postProcess -func 'patchAverage(name=inlet,p)'
    postProcess -func 'patchIntegrate(name=inlet,p)'

Resolves bug-report http://bugs.openfoam.org/view.php?id=2117

The use of the term 'source' in the context of post-processing is
confusing and does not properly describe the process of region
selection.  The new names 'surfaceRegion' and 'volRegion' better
describe the purpose of the functionObjects which is to provide field
processing functionality limited to a specified region of space, either
a surface or volume.

The keyword 'source' is renamed 'regionType' which better describes the
purpose which is to specify the method by which the surface or volume
region is selected.

The keyword to select the name of the surface or volume region is
renamed from 'sourceName' to 'name' consistent with the other
name-changes above.

Resolves bug-report http://bugs.openfoam.org/view.php?id=2112

Added patchIntegrate configuration

Added configuration file etc/caseDicts/postProcessing/fields/writeObjects

createTurbulenceFields: utility replaced by 'turbulenceFields' functionObject used with the '-postProcess' option

tutorials/incompressible/pisoFoam/les/pitzDaily: Added scalarTransport
functionObject to demonstrate the new functionality

to enable the postProcess -func <function> option to work

Patch contributed by Bruno Santos
Resolves patch request http://bugs.openfoam.org/view.php?id=2112