adds iMerit to lookups

[BryonLewis]

Adds the iMerit performer to the lookups to support ground truth annotations. The validator looks like the following:

    @validator('originator')
    def validate_originator(cls, v: str) -> str:
        if Performer.objects.filter(short_code=v.upper()).exists():
            return v
        raise ValueError(f'Invalid originator "{v}"')

The v.upper is why I'm using IMERIT as the short code.