Client settings

- Adding support for rollbar client settings `hostWhitelist` and `ignoredMessages`
- Moved `client_api_key` into the `client_settings` hash.

Additionally, this `client_settings` is a breaking change, so maybe it's time we move smoke_detector to 1.0.0.
we already have an example that checks that the Rollbar JS snippet is inserted into the `<head>` (line 21). Are you talking about that, or maybe just the wording of the expectation?