Compute avg speed per service and aggregate global result for operator

[gmatosferreira]

Determine first and last update for each service (exclude first and last stops to avoid idle buses before service starts) and divide by length between both to get service avg speed. This will be the commercial speed for each service.

[gmatosferreira]

Consider to update https://u-shift.github.io/GTFShift/reference/rt_extend_prioritization.html after

[gmatosferreira]

Methodology suggested by @temospena for trip commercial speed calculation: