Support logs/analytics/tracking as an option for filter state changes

[birm]

TCIA is interested in events like filter change, start download, etc.

[kirbyju]

Yes, we'd be interested in being able to understand:

1. how often people are using the "build a custom cohort and download the slides" workflow for pathology compared to how often they just go download the full collection with an Aspera package to understand workflow preferences.
2. which slides are people downloading most often via this workflow to understand dataset popularity.