Add option to apply a specified force to a mesh wall

A number of applications would benefit from being able to apply a specified force to a mesh wall as a whole. applyForceToMeshWall(..) would apply a net force to the entire mesh, causing it to translate without deforming the mesh. This feature would be the mesh-wall equivalent of applyForceToWall(..) for simple, planar walls. The implementation of applyForceToWall(..) should provide a guide for implementing this feature.