Addition of find_volume to XDG

[pshriwise]

DAGMC and double-down both have an option to find what volume a location is in without looping over all volume trees.

First we should address issue #4 in XDG so that triangle references/surface geometries aren't duplicated. Part of that process will also provide us with the surface sense information on each surface so we can reference it during the find_volume operation.

Once that's complete, then we can look at joining all of the geometries into a single BVH to perform a find_volume operations and avoid a loop over all of the volume trees in the model.

Single BVH creation in double-down: https://github.com/pshriwise/double-down/blob/f85a1ac4e1f450414be2513c3b123d88db2c81d6/src/RTI.cpp#L720-L721
Find volume implementation in double-down: https://github.com/pshriwise/double-down/blob/f85a1ac4e1f450414be2513c3b123d88db2c81d6/src/RTI.cpp#L312