Add additional user actions in Audit events

Adds the additional user events (this does not change the underlying current audit mechanism)

Different approach from https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1927

• Add a new email address
• Remove an email address
• Password change
• Forget password
• Failed to login
• Add SSH key
• Grant Oauth access

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/1370

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together