[FEATURE] Add ID of the last event on an object to the JSON for an object

[wwahammy]

Is your feature request related to a problem? Please describe.
Currently, there's no way to get the last id of the last event that affected an object. As an example, let's say 'evt_1234' was a 'transaction.updated' event on transaction with ID trx_5678. This would be useful for Zapier where they need to have an unique id every time the object is updated.

Describe the solution you'd like
There should be last_event field on every object which has the id of the last event on that object.

In the future, this could be an expandable object but for now, it's not :)