HttpOutcomeException should be created from IPage rather than HttpResult

[roryprimrose]

There is more information about the page that a caller may want to inspect other than just the HttpResult. Exposing this via the exception means that they don't need to consult browser.Page when the exception is thrown.

[roryprimrose]

This won't be implemented because it causes a serialization issue. The page exposed by the exception can't be serialized whereas the HttpResult type has support for this. Serialization of the exception is more important for logging and reporting that is the suggested ease of use.