Handle different logger intervals

[iamambrus]

As noted in the PySoar repository ( GliderGeek/PySoar#121 ) a high logger interval (e.g. 1 sec) can disrupt thermal detection and result in unusable performance indicators.

E.g. check flight PB on https://www.soaringspot.com/en_gb/62th-hungarian-national-gliding-hajduszoboszlo-airport-2017/results/unknown/task-8-on-2017-07-14/daily

The igc_lib repo already has an approach implemented for this:
https://github.com/xiadz/igc_lib/blob/master/igc_lib.py#L978

On a different note would there be a benefit to reuse igc_lib or make the flight analysis 'pluggable'?

[GliderGeek]

Thanks for pointing this out, seems like a good option to implement. Furthermore, i would very much interested to add the igc-lib thermal detector. Seems like a nice library. Maybe we could work together?