Define CVF Models

Define the following models to support the [CVF initiative](https://wiki.corp.adobe.com/display/AEPLT/Customer+Value+Framework).

- Common: a shared component which is utilized by the various CVF schemas. It contains all properties common to the other schemas.
- Segment: a schema which captures relevant AEP Audience data. Augments Common with Segment specific properties.
- Destination: a schema which captures relevant AEP Destination data. Augments Common with Destination specific properties.
- AggregateProfileStats: a schema which captures relevant AEP profile aggregate data. Augments Common with profile specific properties.

Datasets will be instantiated directly from the 3 schemas.

Start by reading the linked CVF initiative documentation to determine the required properties for Common, Segment, Destination, and AggregateProfileStats. Define the four models so the three applicable schemas can be instantiated as datasets, with shared properties represented by Common.

Written by the indexing model from the issue text.