ENH: changing rhoSimpleFoam to rhothermo and bounding thermo.rho between minRho and maxRho.

Bounding thermo.rho in rhoPorousSimpleFoam.
Changing initial time step in externalSolarLoad tutorial.
Commenting out momemtun source term in steamInjection which causes problems

tutorials/multiphase/reactingTwoPhaseEulerFoam/laminar/steamInjection/constant/fvOptions

@@ -43,7 +43,7 @@ options
             }
         }
     }
-
+/*
     momentumSource1
     {
         type            vectorSemiImplicitSource;
@@ -55,11 +55,11 @@ options
             volumeMode      absolute;
             injectionRateSuSp
             {
-                U.steam           ((0 1e-1 0) 0); // kg*m/s^2
+                U.steam           ((0 1e-2 0) 0); // kg*m/s^2
             }
         }
     }
-
+*/
     energySource1
     {
         type            scalarSemiImplicitSource;