Lands the stacked web PRs #75, #79, #80, #81, #83, #85, #87, #89, #92, #95 and #99 in one squash. Server counterparts #166-#176 are merged. Remaining review items follow in a fix PR.
Airtime telemetry is on-air seconds, so chart it as a percent of elapsed time.
Add channel busy, packets heard, SNR heard and payload type charts from the
new per-observer activity endpoint; hidden until the server has it.
MrAlders0n