Add GROVER LM + fix some bugs

[fteufel]

This PR adds the GROVER DNA LM and fixes some issues.

• GROVER added (embedder, tokenization using max match algorithm, auto download util for zenodo)
• Fix some bugs for variant effect prediction (#48 #49)
• Fix an indexing bug in variant effects prediction with AWD-LSTM
• Standardize load_checkpoint in hydra config to False
• Fix epochs: 100 for enhancer annotation
• Changed metrics computation in the trainer class to always handle lists, with the summary metric returned in metrics[0]