GPXIN-11: Stationary time calculations may be inaccurate

The calculation of time stationary may be inaccurate;

|time|speed|
|10|20|
|20|20|
|30|0|
|40|0|
|50|5|

If the chart above was used, GPXIngest would calculate a stationary time of 20 seconds ((30 - 20) + (40-30)) .

However, during (at least some of) the 10 seconds between 20 & 30, the vehicle would have been decelerating.

Really what needs to happen, is we need to look at whether the last speed was 0, and consider the block moving time if not. So the car in the chart above would have been stationary for around 10 seconds, and moving for 30

Obviously we might actually have been stationary for slightly longer, but there's no way to know how far into the interval we either stopped or started moving, so it seems better to lock it to the interval's beginning so that the maths at least follows more easily in your head.