This commit adds the requisite backing storage and parser support
for capturing and transporting simulator-level calculation of phase
and mixture density value for purpose of summary file output. To
this end, make 'SegmentQuantity' into a template on a set of defined
items and make SegmentPhaseQuantity into a specialisation of this
template. Add a new specialisation, SegmentPhaseDensity, which
holds phase densities (oil, gas, water), and fluid mixture densities
with and without flowing fraction exponents.
These will be used to transport the values needed to output segment
level summary vectors
SDENx -- Phase density of phase 'x' (O, G, W)
SDENM -- Fluid mixture density without flowing fraction exponents
SMDEN -- Fluid mixture density with flowing fraction exponents
e7226d4ca8