Instance state, fix sharing, Durable objects.

Remember instance state across configuration changes, and enable
rotation.  This remembers current modes and in-progress traversals.

Always finish action modes after launching an action.  Fix sharing
by always putting Uris in extras, and always wrap in a chooser.  Find
common MIME types when sharing multiple documents.  Fix downloads
launching by following directory MIME type change.

Introduce "Durable" which is like Parcelable, but can be used for
both byte[] storage and Parcel transport.  Make both DocumentInfo
and DocumentStack durable.

Disable recents until new behavior is implemented.

Bug: 10460236, 10446265, 10533674, 10456344, 10456702
Change-Id: I4eaf2b0b4cde611c69a1e7b5f1586f6b02019b27