Add example for tokenizing .loom dataset

Update gene classification example to create directory after training arguments are defined

Subclass collator for cell classification

Update pretrainer for transformers==4.28.0

Add example input labels for distinguishing bivalent promoters.

Add in silico perturbation example notebook.

Add example input files for gene classification of TF dosage sensitivity

Add example for hyperparameter optimization for disease classifier

Add data collator for gene classification and example for gene classification

Add data collator for cell classification and example for cell classification

Add Geneformer trainer and pretraining example