Provided by Juho Peltola

and two-phase functionality separated from multiphase functionality

Currently this is implemented only for the Antoine equation, for the
other more complex models an iterative inversion from pressure to
temperature is required.

In preparation for adding the Tsat function

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.

twoPhaseEulerFoam/interfacialModels/heatTransferModels/sphericalHeatTransfer: new heat-transfer model

Model which applies an analytical solution for heat transfer from the
surface of a sphere to the fluid within the sphere.

Provided by William Bainbridge

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