Update Probe Viewer based on the Neuropixels-PXI changes

[bparks13]

Can we open an issue on the main probe viewer code, wherever that is, that requests that left tick marks on the the viewer are labelled with the physical depth along the probe in um?

Originally posted by @jonnew in #89 (review)

[bparks13]

There have been some important changes to the ProbeViewer in the Neuropixels PXI plugin, including adding depth to the probe viewer as this issue originally requested.