Add chi square analysis for query logs

[tballison]

It can be very useful to look for emerging queries by comparing one quarter's data to another or one timeframe's to another. One can do this with Solr or Elasticsearch or OpenSearch's Significant terms query, but sometimes users don't have their queries loaded into these engines, and they just have an xlsx spreadsheet.

This proposal is to add a simple chisquare calculation to compare a foreground worksheet vs background worksheet within a single xlsx workbook.