solvers::multiphaseEuler: New solver module for Euler-Euler multiphase simulations

executed with foamRun for single region simulations of foamMultiRun for
multi-region simulations.  Replaces multiphaseEulerFoam and all the
corresponding tutorials have been updated and moved to
tutorials/modules/multiphaseEuler.

Class
    Foam::solvers::multiphaseEuler

Description
    Solver module for a system of any number of compressible fluid phases with a
    common pressure, but otherwise separate properties. The type of phase model
    is run time selectable and can optionally represent multiple species and
    in-phase reactions. The phase system is also run time selectable and can
    optionally represent different types of momentum, heat and mass transfer.

    Uses the flexible PIMPLE (PISO-SIMPLE) solution for time-resolved and
    pseudo-transient and steady simulations.

    Optional fvModels and fvConstraints are provided to enhance the simulation
    in many ways including adding various sources, Lagrangian
    particles, surface film etc. and constraining or limiting the solution.

SourceFiles
    multiphaseEuler.C

See also
    Foam::solvers::compressibleVoF
    Foam::solvers::fluidSolver
    Foam::solvers::incompressibleFluid

tutorials/modules/multiphaseEuler/bubblePipe/validation/createGraphs

@@ -0,0 +1,50 @@
+#!/bin/sh
+
+if ! which gnuplot > /dev/null 2>&1
+then
+    echo 'gnuplot not found - skipping graph creation' >&2
+    exit 1
+fi
+
+time=$(foamListTimes -case .. -latestTime)
+
+graphFile=../postProcessing/graph/$time/line.xy
+
+gnuplot<<EOF
+    set terminal postscript eps color enhanced font "Helvetica,20"
+
+    set output '../void_fraction.eps'
+
+    set xlabel 'r (mm)'
+    set ylabel '{/Symbol a} (-)'
+
+    plot "$graphFile" u (\$1*1000):4 w l lw 3 lc rgb 'black' t 'total',\
+         "$graphFile" u (\$1*1000):2 w l lw 2 lc rgb 'green' t 'd < 5.5mm',\
+         "$graphFile" u (\$1*1000):3 w l lw 2 lc rgb 'red' t 'd > 5.5mm'
+
+    set output '../nonDragForces.eps'
+
+    set ylabel 'F_{r} (N/m^3)'
+
+    plot "$graphFile" u (\$1*1000):(-\$5) w l lw 2 t 'Lift',\
+         "$graphFile" u (\$1*1000):(-\$8) w l lw 2 t 'Wall lubrication',\
+         "$graphFile" u (\$1*1000):(-\$11) w l lw 2 t 'Turbulent dispersion'
+EOF
+
+injectionFile=../postProcessing/probabilityDensity.injection/$time/probabilityDensity.injection.xy
+outletFile=../postProcessing/probabilityDensity.outlet/$time/probabilityDensity.outlet.xy
+
+gnuplot<<EOF
+    set terminal postscript eps color enhanced font "Helvetica,20"
+
+    set output '../volumeDensity.eps'
+
+    set xlabel 'd (mm)'
+    set ylabel '({/Symbol a}/{/Symbol a}_{tot})/{/Symbol D}d (mm^{-1})'
+    set xtics 1
+
+    plot "$injectionFile" u (\$1/1e-3):(\$2/1e3) w histeps lw 3 lc rgb 'green' t 'injection',\
+         "$outletFile" u (\$1/1e-3):(\$2/1e3) w histeps lw 3 lc rgb 'red' t 'outlet'
+EOF
+
+#------------------------------------------------------------------------------