Update Event schema to have note array (as in OCDEP4)

http://opencivicdata.readthedocs.org/en/latest/proposals/0004.html#id1

```
    notes
        List of strings, which store any notes taken during the event while discussing this item.
```

Just changing a string to a list of strings. Anyone see an issue here?
Uh, whoops. Fixing this up now.