Make an unconfirmed interpolation curve remaining even if you switch datasets

[yu-smc]

As-Is

If you change datasets, with an interpolation curve which is not confirmed, the curve data will be completely deleted

To-Be

It should be way better if the interpolation curve remains on the screen even if you change datasets, and when you click 'confirm' button of the interpolation feature, the actual points data will be registered in the active dataset at that moment.

Notes

Need to solve the issue #153 to handle this problem because the interpolation data must be completely independent from a certain dataset to achieve the above specifications