Consider integrating enriched API and web event classes

We've started an object-oriented approach to organizing useful attributes of the API and web event dicts [over in `scrapers-us-municipal`](https://github.com/opencivicdata/scrapers-us-municipal/blob/2ee2c55d69150c7440487d9606b4a27b812d94b4/lametro/events.py#L249-L299). If these attributes are generally useful, it could be cool to have them here.