Improved overlap checker

[Waqar-ukaea]

Draft PR to add an algorithm for checking overlaps along geometry edges to the overlap checker tool.

Current state:

• Loops over all triangles and fires rays from every triangle vertex fires a ray along the edge checking for an intersection with a surface belonging to a volume that is not the parent volume of the triangle. This works and correctly identifies intersections where I would expect. However...
• There are additional intersections detected from rays that are launched from one volume and collide with another volume (as they are not stopping at the boundary of the volume they are launched from) leading to intersections on the other volume (see image below).
• Perhaps the extra intersections are inevitable due to the way rays travelling along surfaces are handled but I would need a way to isolate the intersection points of interest (where the edges overlap) - not sure how I would do this just yet.
  
• Explicitly refers to elements as triangles - should probably change variable names to reflect generic elements. In theory this shouldn't require any logic changes just nomenclature.
• By default the overlap-check tool will only check for overlaps on vertices but edge checking can be enabled by passing flags -e or --check-edges at runtime.
• Lots of extra fluff in writing things out to files and stdout which needs to be removed before merging into main.
• Missing a progress bar.
• Missing support for openmp parallelism over the new algorithm.
• Added skeleton for an additional test in the overlap checker tests. This currently doesn't test for anything but is in place ready for once I am happy with the edge algorithm for the overlap checker. The test relies on the geometry added in PR#3 for the xdg_test_files repo.

[pshriwise]

I updated the test files submodule here and included the symbolic link line for the test in the CMakeLists file. I'll do a more thorough review soon if you feel like this is ready to go @Waqar-ukaea