dynamicMotionSolverListFvMesh: New mesh-motion solver supporting multiple moving regions

e.g. the motion of two counter-rotating AMI regions could be defined:

dynamicFvMesh   dynamicMotionSolverListFvMesh;

solvers
(
    rotor1
    {
        solver solidBody;

        cellZone        rotor1;

        solidBodyMotionFunction  rotatingMotion;
        rotatingMotionCoeffs
        {
            origin        (0 0 0);
            axis          (0 0 1);
            omega         6.2832; // rad/s
        }
    }

    rotor2
    {
        solver solidBody;

        cellZone        rotor2;

        solidBodyMotionFunction  rotatingMotion;
        rotatingMotionCoeffs
        {
            origin        (0 0 0);
            axis          (0 0 1);
            omega         -6.2832; // rad/s
        }
    }
);

Any combination of motion solvers may be selected but there is no special
handling of motion interaction; the motions are applied sequentially and
potentially cumulatively.

To support this new general framework the solidBodyMotionFvMesh and
multiSolidBodyMotionFvMesh dynamicFvMeshes have been converted into the
corresponding motionSolvers solidBody and multiSolidBody and the tutorials
updated to reflect this change e.g. the motion in the mixerVesselAMI2D tutorial
is now defined thus:

dynamicFvMesh   dynamicMotionSolverFvMesh;

solver solidBody;

solidBodyCoeffs
{
    cellZone        rotor;

    solidBodyMotionFunction  rotatingMotion;
    rotatingMotionCoeffs
    {
        origin        (0 0 0);
        axis          (0 0 1);
        omega         6.2832; // rad/s
    }
}

tutorials/mesh/foamyHexMesh/mixerVessel/constant/dynamicMeshDict

@@ -15,11 +15,13 @@ FoamFile
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-dynamicFvMesh   solidBodyMotionFvMesh;
+dynamicFvMesh   dynamicMotionSolverFvMesh;
 
 motionSolverLibs ( "libfvMotionSolvers.so" );
 
-solidBodyMotionFvMeshCoeffs
+solver solidBody;
+
+solidBodyCoeffs
 {
     cellZone        rotating;