Merge with storage

[jakearchibald]

whatwg/storage#18

Service worker registrations and cache storage should be linked to a particular storage bucket.

This explains how origin storage is purged, and makes it clear that these items are protected by persistent storage.

[annevk]

@jakearchibald @jungkees I'd greatly appreciate your input on whatwg/storage#18 (comment). I'd like to make progress on this as clarifying how storage is keyed, how it gets removed, and potentially replaced is becoming rather important.

[wanderview]

FYI, I added storage keys to service worker spec to support partitioning, but I missed adding references to bottle maps, etc. This probably needs to be moved to the bottle map to be correct:

https://w3c.github.io/ServiceWorker/#dfn-request-response-list