povolny1

It may be worth noting that we're planning on adopting the following hierarchy for multibody problems (PR on the GEOSX side: https://github.com/GEOSX/GEOSX/pull/1742): ``` ```

@biagas Apologies for the late reply - yes, ideally we'd like to be able to simultaneously plot independent fields from 'backgroundGrid' and 'particles.' Also, all the elements in a region...

I'm hoping to get the .vtm hierarchy finalized soon. @biagas What would be the best way to go about testing your changes? Should I just send you a dataset?

This PR will require a rebaseline of all integrated tests due to the `ParticleManager` being registered on `MeshLevel` by default, similar to all other managers.

`integratedTests` have been rebaselined [here](https://github.com/GEOSX/integratedTests/pull/226)

Unit test is implemented and passing, I will make an accompanying PR for GEOSX soon