altosui: Make scan UI handle incremental telem data

altosui: Make scan UI handle incremental telem data

The new telem format doesn't send everything in each telem packet, so
we need to handle updating information incrementally in the scan
results. This involved clearing old scan data when switching
frequencies and then updating existing entries with new data as it arrives.

Signed-off-by: Keith Packard <keithp@keithp.com>