Scan schemas for new fields and add support for them

[mesozoic]

Before:

% python scripts/find_model_changes.py
pyairtable.models.comment.Comment is missing field: attachments
pyairtable.models.schema.BaseCollaborators is missing field: packageInstallations
pyairtable.models.schema.TableSchema.DateDependency is missing field: isForwardOnly
No unscanned classes found in scanned modules

After:

% python scripts/find_model_changes.py
No missing/extra fields found in scanned classes
No unscanned classes found in scanned modules