DC Offset Filters

[kkappler]

This is not strictly required for MT, since we are not sensitive to DC Levels, however there are several systems that use DC Magnetometers, for example flux-gates. To make working with these data easier and sanity checking for example orientation via total field projections on various components it makes sense to have an optional filter that corrects for static shift in a measurement.

This would be like the Time Delay Filters in that it is applied in Time Domain, not in frequency domain.