Beter support for shrinkwarp in retopology

At this moment, shrinkwarp works fine under certain workflows, but have no support to others.

By default, the modifier is design to work with one mesh and ONE object in reference, what works, but doesn't work fine when the reference object have more than one mesh inside.

Example: ONE object with TWO meshes.

Current result creates some kind of "safe region" where the meshes overlap each other.

With better support for this kind of workflow, the re-topology process will have a huge improvement, since sculpt mode can be used to tweak the projected base mesh.

A brush can move, relax, smooth and etc, and the modifier can keep the vertex attached to the reference object.

With single brushes instead of vertex, edge, faces alignment in edit mode the entire workflow can have a speed boost.

Here a example of a personal project. The reference object contain a head mesh, a ear mesh, arm mesh, torso mesh, one mesh for each finger in hands and feet, and a mesh to the legs, 15 different meshes in one object.

The modifier works almost perfect for this kinda of workflow, but a little tweak in the code and it can be a perfect modifier for re-topology.

This can also creates a more flexible workflow, since mix something in the shape, doesn't require to edit the re-topology most of the time, since things like, enlarge muscles or fat areas or change the length of something will automatically reshape the reference mesh.