nan mode summaries in older data

[Abby-Wheelis]

Two issues seem to be related:

1. public dashboard #142
2. op-admin-dashboard #120

These both relate to an error that "float is not subscriptable" when attempting to get the max mode from the summary. A quick patch on the public dashboard will be able to un-break the affected deployments, but this raises a larger issue with the data that we should investigate.

Why are some of the mode summaries nan? This seems to be related to older deployments, is there some sort of backwards compatibility piece that is missing?