Added mixins.py with all the Cannot and Has atrributes

Summary: Created a new file mixins.py that has all the attributes multiple objects share

Test Plan: Tested locally on my machine
Added promoted_object to adset and bumping version to 2.2.0

Summary:
- Added promoted_object to adset
- Removed comment from config.json.example
- Bumped versions

Test Plan: read diff
Added changes to Custom Audience and Reach and Frequency Predictions

Summary:
Added changes to Custom Audiences, breaking changes to R&F. Added R&F object
(since it was missing). Added test for CA.

Test Plan:
Run unit test.
Run integration test.

python -m facebookads.test.unit
python -m facebookads.test.integration <ACCESS_TOKEN>