Incorrect flight segmentation with landing instability

[sco1]

While the flight segment detection logic from b20f785 seems to do a good job mitigating noise on takeoff, it does not correctly account for noise on landing.

In this example, the start of flight segment 2 is incorrectly defined in the noisy region of flight segment 1's landing:

While the ultimate fix may be a side effect of the logic for #1, as a starting point we probably need to use a time threshold between segments to determine when to turn off the segment merging flag rather than just assuming that the landing data is clean.