esowc/ecPoint-Calibrate: v0.25.0

This is a standalone release to allow merging non-leaf decision tree nodes with a single click. This was achieved by introducing a new mode called "Merge children" (see below).

<img width="436" alt="Screenshot 2021-04-14 at 05 02 04" src="https://user-images.githubusercontent.com/3684187/114633741-68743700-9cc1-11eb-9570-5ff494cc4dac.png">

It will work for arbitrarily nested trees and is a destructive operation (no way to undo). Once merge is finished, you must change the mode to "Simple" or "Non collapsible" in order to view the MFs.

⚠️ While this is a new mode, it impacts the creation of weather types in the other modes as well (i.e., "simple", and "Non collapsible"). Normally, the feature should work seamlessly, but please watch out for the following class of bugs just to be sure:

• Issues with the MFs, titles, codes of the weather types after the merge operation.
• Issues with the threshold breakpoints table after the merge.
• Merge operation affecting unrelated branches of the decision tree.