Handle new RepositoryEvent actions

Summary:
GitHub introduced new events:
https://developer.github.com/changes/2016-04-18-new-webhook-actions-are-live/#list-of-comprehensive-changes

This commit allows to handle deleted/publicized/privatized actions.

Fixes T935.

Test Plan: Unit tests updated.

Reviewers: dereckson

Subscribers: alken-orin

Maniphest Tasks: T935

Differential Revision: https://devcentral.nasqueron.org/D571