Issue #32: Add support for SSL certificate management.

[jlfranklin]

Reopening #33.

Add support for the following endpoints:

get_ssl_settings(): /environments/{environment_uuid}/ssl
get_ssl_certs(): /environments/{environment_uuid}/ssl/certificates
get_ssl_cert(): /environments/{environment_uuid}/ssl/certificates/{cert_id}
install_ssl_cert(): /environments/{environment_uuid}/ssl/certificates (POST)
delete_ssl_cert(): /environments/{environment_uuid}/ssl/certificates/{cert_id} (DELETE)
activate_ssl_cert(): /environments/{environment_uuid}/ssl/certificates/{cert_id}/actions/activate (POST)
deactivate_ssl_cert(): /environments/{environment_uuid}/ssl/certificates/{cert_id}/actions/deactivate (POST)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.