restore: Clean up blobs that are not related to a file in state
restore: Clean up blobs that are not related to a file in state

This patch makes sure only blobs that are referenced by the localStorage
state are actually restored. Blobs that are returned from the persistent
serviceWorker or IndexedDB stores, but aren't referenced by the `files`
state object restored from localStorage, will be deleted.

Should fix #348.
Part of #342, but we need to do more before we can call that fixed :)

transloadit/uppy,transloadit/uppy,transloadit/uppy,transloadit/uppy