This patch:
- migrates navigation watcher to use protocol-issued lifecycle events.
- removes `networkIdleTimeout` and `networkIdleInflight` options for
`page.goto` method
- adds a new `networkidle0` value to the waitUntil option of navigation
methods
References #728.
BREAKING CHANGE:
As an implication of this new approach, the `networkIdleTimeout` and
`networkIdleInflight` options are no longer supported. Interested
clients should implement the behavior themselves using the `request` and
`response` events.
