- Add colors for observers in sensor parameter plots
- Bugfix with observer positions
- sensor_delta is separate plot now

TDC change from old to new observatory 2018, change of iaf header during
year
SHE the correct header, WORK was wrong

- Allow to exactl match NaN
- Allow to interpolate NaN using filter
- TODO: Add percentage of data that must be available to
        produce value

- Data of day was set to next days data if filter applied
- This bug was introduced with commit 3c5b577b on 2020-01-06
- No definitive data was affected by this bug

- Find rotation and scale values between the variometers
- Use stochastic inversion

- setnan: Set all data outside of filter range to NaN
- linear: Linear extrapolation before filtering
- none:   Return shorter vector

First unadapted version of tools inherited from programs
by Achim during stay at ETH.

Find timeshift and relation between FGE sensor temperature readings
and delta-F variations. Create plot for evaluation.

Despike routines for data vector, and for cdf-files where data
will be flagged. Despiking is based on two median filters:
- Filter 1: Low order, lower threshold, for individual spikes
- Filter 2: High order, larger threshold, for multiple consecutive
            spikes