This change follows the pattern of our cookies persistence
implementation: the "browser" process is responsible for interacting
with the sqlite database, and WebContent communicates all storage
operations via IPC.
The new database table uses (storage_endpoint, storage_key, bottle_key)
as the primary key. This design follows concepts from the
https://storage.spec.whatwg.org/ and is intended to support reuse of the
persistence layer for other APIs (e.g., CacheStorage, IndexedDB). For
now, `storage_endpoint` is always "localStorage", `storage_key` is the
website's origin, and `bottle_key` is the name of the localStorage key.
Instead of storing all storage objects in static memory, we now
follow the the spec by lazily creating a unique Storage object
on each document object.
Each Storage object now holds a 'proxy' to the underlying backing
storage. For now, this proxy is simply a reference to the backing
object. In the future, it will need to be some type of interface
object that stores on a SQLite database or similar.
Session storage is now correctly stored / tracked as part of the
TraversableNavigable object.
Local storage is still stored in a static map, but eventually this
should be factored into something that is stored at the user agent
level.
