Improve layout of nodes in provenance-ui

[libpitt]

Currently, the graph loads like:

Ideally, it should look like:

There are two issues here:

1. The nodes are on the same y value regardless of immediate children length.
2. The edges are crossing each other. Since we actually have graphs and not trees, with the level order nodes list, we should also consider the paths to the leaf nodes and their respective depths. Perhaps keeping paths of similar depth relative to the level order could improve the visual output.

[maxsibilla]

Reopening this card. We may want to attempt to address this in the near future as the Provenance UI is consistently highlighted during demonstrations of the portal. As the portal continues to grow with larger provenance chains the current default layout could become an issue (see https://data.sennetconsortium.org/source?uuid=0564b752325dfdf5e7feb9050595ff1f/)