Add HEROHE downstream task (Her2)

[roman807]

Add HEROHE as downstream task: https://ecdp2020.grand-challenge.org/Dataset/ to identify Her2 (slide level task, binary classification, 500 training / 362 test samples)

Background info: HER2 is a protein receptor which is amplified/overexpressed in approximately 15–20% of breast cancers. Overexpression is associated with aggressive behavior and high probability of response to HER2 targeted therapy.