More configuration options for OoyalaCachePlugin.

Now client code can configure cache control settings like max-age and stale-if-error. Removed Cache-Control configuration from the OoyalaClient class.
Clean up the OoyalaClient.

- Moved OoyalaClient::onCommandBeforeSend() event to OoyalaSignature plugin.
- Set timeouts to 0 for tests.
Add inline comments for configuration.

Going to add some documentation eventually...