yasmine writes pole (and zero) values as plusError and minusError after NRL sensor import

[metempleton]

I created a new stationXML using the wizards, selecting a Streckeisen STS-1 for the sensor. Although the NRL RESP file
includes values of 0.0 for plusError and minusError, yasmine assigns the pole (or zero) value to these attributes and includes
them when writing out stationXML:

          <Pole number="0">
            <Real minusError="-0.01234" plusError="-0.01234">-0.01234</Real>
            <Imaginary minusError="0.01234" plusError="0.01234">0.01234</Imaginary>
          </Pole>

Desired default behavior would be to omit plusError and minusError attributes for nominal responses (but allow the user to
insert and assign them during editing, if desired). Note that NRL v2 does not include error values when they are zero (which is
always for nominal responses).