Introduce reception outage tolerance

[Turbo87]

When doing live scoring the OGN/Flarm reception at the turnpoints might not be great so valid turns might not be seen by the OGN receivers. Adding some tolerance to the scoring might be valuable so that "almost reached the turnpoint" will still be scored in live scoring mode.

One idea would be to estimate how bad the reception on each leg is (e.g. assume a GPS fix every 10sec, if there are gaps of more than 10sec sum them up and divide by total time on the leg, resulting in a reception loss percentage), and then introduce a tolerance based on that percentage. If for example 30% of the time on the current leg there was no reception then the turnpoint could have a tolerance of 30% of the leg length. We might have to cap this (e.g. at 50% or similar) to not give too much tolerance though.

/cc @dspreitz

[dspreitz]

Here are some example files, which should help develop this feature.
Contest: Bayreuth 2018
Day: 2018-05-30
Class: Open

The file contains:

• Normal IGC files used for official scoring
• IGC files generated from OGN data
• task file
• filter file
• Official task sheet as pdf
• Official scoring as pdf

Bayreuth_2018-05-30_Open.tar.gz