* Rename from DiffCurve to CalculatedCurve and add operators selection
* Add option to select depth source for resampling in CalculatedCurve
- Select source for depth values for resampling
- Depths from first curve, second curve or union of these
- Added unit tests for function creating union depth values and calculate value with selected operator.
* Guard divide by zero
* Adjust algorithm for union of depths
- Prevent duplicated depth values (no need for enter/exist of k-layer when resampling)
- Add threshold for depth distance
- Update unit tests
