Periodically save post when editor is open, for Doomsday scenarios

[vickychijwani]

In what I call Doomsday scenarios (like OS crashes, 0% battery, etc), the user may lose their edits if onPause isn't called. We can pre-emptively save edits (for both drafts and published posts) locally to minimize data loss. This auto-saving may happen periodically, or after the user stops editing the post for x seconds, or with some other policy.

[vickychijwani]

See #144 for a caveat to this.