Add additional dataset to district0x mapping example

[Zerim]

This PR makes the following changes:

• Adds a full event signature to the data source definition, because Solidity supports overloading event names
  • Adds another top level data set, to reflect an additional "top level" contract being used to emit events, and load data.
  • Moves "kind" to the same level as "data" and "mapping" since it seems to refer to the entire dataset rather than just the data.