Resolves bug-report http://openfoam.org/mantisbt/view.php?id=1899

and two-phase functionality separated from multiphase functionality

to simplify construction of dimensionedScalar properties and avoid the
duplication of the name string in the constructor call.

Multi-species, mass-transfer and reaction support and multi-phase
structure provided by William Bainbridge.

Integration of the latest p-U and face-p_U algorithms with William's
multi-phase structure is not quite complete due to design
incompatibilities which needs further development.  However the
integration of the functionality is complete.

The results of the tutorials are not exactly the same for the
twoPhaseEulerFoam and reactingTwoPhaseEulerFoam solvers but are very
similar.  Further analysis in needed to ensure these differences are
physical or to resolve them; in the meantime the twoPhaseEulerFoam
solver will be maintained.

This is necessary to guarantee consistency between the residualAlpha
used for drag and buoyancy in a multi-phase system