Add option for time window masking analyzer data

[holukas]

At the Davos site, the QCL gas analyzer does not always sample air from the eddy covariance inlet. Nevertheless, analyzer data are continously streamed to the binary EC file, regardless of the selected air stream input. In addition, there is no flag or any other method to check for the inlet in the binary EC data. Thus, it would be beneficial to be able to mask out time windows, where the analyzer data should not be used for flux calculation.

• multiple cron-like entries
• what to do with the analyzer data in the masked windows? NaN or just repeating the last valid record? Leave this as an option?

[holukas]

I think this is a special case that should be handled outside of bico.