[ServiceWorker] A way to control which client (or type of client) receives a navigation (#758)

Sometimes the user expresses how they want a link to be opened, eg "open in new tab" or pasting a link into an existing window, but other times it's ambiguous, such as clicking a link or tapping a notification that subsequently calls `openWindow`.

This should allow developers to create single and multi-document applications by determining how links are handled.

Some patterns to enable:

User clicks on a link in a native app, developer wants it to launch in a new chromeless window (the user has already added this site to homescreen).

User clicks on a link on a website, developer wants to focus an existing client and target the navigation at it.

User clicks on a notification, developer wants to focus an existing client, discard the navigation, and postmessage the client.

User clicks on a homescreen icons, developer wants to create a new chromeless client, even though there's an already-open client for the target url.

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/758