tutorials/lagrangian: Added mixedVesselAMI2D

This tutorial demonstrates moving mesh and AMI with a Lagrangian cloud.
It is very slow, as interaction lists (required to compute collisions)
are not optimised for moving meshes. The simulation time has therefore
been made very short, so that it finishes in a reasonable time. The
mixer only completes a small fraction of a rotation in this time. This
is still sufficient to test tracking and collisions in the presence of
AMI and mesh motion.

In order to generate a convincing animation, however, the end time must
be increased and the simulation run for a number of days.