Add emotion to audformat.define

[schruefer]

To ensure consistent naming of emotions, it would be handy to include Emotions in audformat.define.
see: https://audeering.github.io/audformat/api-define.html
e.g. audformat.define.Emotion.ANGER

Required emotions are: neutral, anger, disgust, fear, happiness, sadness, surprise, boredom, contempt, admiration, amusement, tenderness, despair, pride, shame, anxiety, interest, irritation, joy(synonym of happiness?), pleasure, relief

Other possible emotions: mildly friendly, mildly unfriendly, very friendly, very unfriendly, negative(negativity), positive(positivity)
Other possible labels: no_agreement, other

Feel free to continue this list!

[hagenw]

We had an internal discussion on unifying the emotion schemes. There we decided to select anger, happiness, neutral, sadness. But maybe it would make sense to add more then those four and including them in audformat would also document how we decided to name them.

@audeerington does this make sense or should we document it at another place?
Could you also write which emotions you think we should include in a possible list.

[frankenjoe]

Maybe we should use a dictionary to support synonyms? E.g.:

{
     'anger': 'anger',
     'angry': 'anger',
     'angriness': 'anger',
     ...,
}

[audeerington]

Yes, I think it makes sense to add the labels here.

As for list of emotions, the emotions that we have used before are:
admiration, amusement, anger, anxiety, boredom, calm, confusion, contempt, despair, disgust, excitement, fear, frustration, happiness, interest, irritation, joy, neutral, pleasure, pride, relief, sadness, shame, surprise, tenderness

For completion we could include them all, but it might be enough to include the ones occurring more commonly in databases:
anger, boredom, contempt, disgust, excitement, fear, frustration, happiness, interest, neutral, sadness, surprise.

Joy/happiness is difficult... so far we have handled them as synonyms, but in some studies they are treated as separate categories (joy being more elated, and happiness more quiet). I would stick with what we have done in the past here and only use the happiness label for both.