Improve `Hotspot Details` dashboard

[jamiew]

One of my favorite dashboards

https://etl.dewi.org/dashboard/7-hotspot-details

• [ ] fill in missing dates so that the ranges are all consistent (e.g. if 30 days selected, show 30 points on x axis)
• [x] fix up my insane nearby hotspots queries to allow specifying a specific as the center, rather than a raw lng/lat
• [x] fix slow challenge queries - avoided in query and fixed by PR https://github.com/jamiew/helium-etl-queries/issues/12

stretch goals

• [ ] allow specifying multiple hotspots at once (using FIlter Field)
• [ ] allow specifying multiple owner addresses and aggregate stats for all of those hotspots