Need ability to undo point adding and effect of callbacks

[jni]

During a call with @andreasmarnold, we discussed what else we needed in affinder before publishing. The big issue he identified is that it is very hard to recover from misclicks: if you inadvertently add an incorrect point (or for example, put down the first three points in the wrong order in the first layer switch), the transform is very distorted and it becomes very hard to recover, even if deleting the points.

This could be fixed by an affinder-level history, where each point added and resulting transform is recorded. When hitting undo, we would switch back to the previous state. Even for long click sequences this would be a small amount of data so not too onerous to keep track of.