Add uncertainties to inventory values (lat, lon, azimuth, dip...)

[jordi-domingo]

This is a suggestion of improvement for future versions:

What about adding uncertainties (lowerUncertainty / upperUncertainty) to the values (lat, lon, azimuth, dip...) of the inventory objects (Station, Stream...).

These kind of uncertainties already exist in the event-related information (Origin, etc.). FDSNXML allows the use of them (minusError / plusError). It would be useful that SC3 also parses / stores / provides them.

I guess it is a big change (involves DB schema), but not difficult technically. Thanks for considering it.