Refactor storage for better migration and kernel switching #22
Description
Currently, each kernel saves data in its own way. So currently if I want to switch one kernel to another I need to drop all the data. It can be really good if we can re-use some of data.
Actually, I don't think we'll have support between e.g KNN and Logistic regression, so on changing the kernel we'll need to drop model data and re-train new model.
In any case, we'll need to draw a diagram on how storage should interact with kernels.
- introduce versioning of kernels and migration from one version to next on upgrade