Fix JNLBA dataset
Fix #3089. @albertvillanova all tests are passing now. Either you or @lhoestq can review it!
As mentioned in #3089, I've added more tags and also updated the link for dataset which was earlier using a Google Drive link. 
I'm having problem with generating dummy data as `datasets-cli dummy_data  ./datasets/jnlpba --auto_generate --match_text_files "*.iob2"` is giving `datasets.keyhash.DuplicatedKeysError: FAILURE TO GENERATE DATASET !
` error. I'll try to add dummy data manually.