Fix emotion description
Fixes the description of the emotion dataset to reflect the class names observed in the data, not the ones described in the paper.

I also took the liberty to make use of `ClassLabel` for the emotion labels.
Hello, I probably have a silly question but the labels of the emotion dataset are in the form of numbers and not string, so I can not use the function classification_report because it mixes numbers and string (prediction). How can I access the label in the form of a string and not a number? 
Thank you in advance.