Can not access iFrames with a src attribute that has a different host.

[aarondufall]

Describe the bug

When the browser finds an iframe in the DOM, it publishes a Page.frameAttached event, then Ferrum takes the params and uses them to create a Frame object that adds to a collection of frames on the current Page object.
When the src URL for the iFrame contains a URL with a different host to the parent, it fires a Page.frameDetached with reason swap .
Then, a Target.targetCreated with type IFrame is published, followed by a Target.targetInfoChanged event. From what I can tell, looking at the Ferrum source code, it doesn't handle type IFrame.

In the contexts#subscribe, all the event handlers have this line, causing type IFrame to be ignored

next unless info["type"] == "page"

To Reproduce
Goto a page where the iframe src attribute has a different host to the main page.

Expected behavior
Access the iframe using the target id in the collection of Frame objects on the main Page object