ADDED:
Second set of coltrols and methods to REIXSXESImageInterpolationAB and
REIXSXESImageInterpolationABEditor to allow the second curve to be
configured.

REMOVED:
uses to of shiftPosition*_ in favour of correlation*CenterPx_ - should
be easier to use, will have to test this concept on users though.

TODO:
-Add the seconf fitting range and fit curve to the plot within
REIXSXESImageInterpolationABEditor
-Test regorously