179-add-hierarchical-croptype-picker

[cbutsko]

Possible TODOs for separate branches:

• introduce a minimum threshold for class count
• add suggestion on how to proceed if too few classes are found (e.g. "Select bigger window", or "Increase the buffer size")
• add select/deselect all button for lower level
• guide to the legend description

[jdegerickx]

Instead of reviewing the code itself, I just tried it myself in a notebook. Seemed to work fine, except for the samples_threshold...

Some observations:

--> when I only select maize among the cereals class, I intuitively expected all other cereal classes would get grouped into an "other cereals" class. Instead, these cereals get merged into "other_temporary_crops". I guess this is because we do not support hierarchical crop type models (yet). Fine with me, we should just document this very clearly in the notebook...

• samples threshold did not seem to work correctly?
  

• In its current state, a user can train a model with 2 classes, one containing 1000 samples and the other containing 10. Shouldn't we protect the user from such models? And perhaps implement a minimum sample amount per class?