polish the code that marks new as unresolved

Previously, because `mark_new_as_unresolved` was hooked on `save_post`, it would cause edits to fire the action and thus re-change the state to new. This resulted in edits to a post to act as if this was a new post.

This fixes the problem by hooking into post transitions instead.
Merge pull request #29 from jkudish/master

polish the code that marks new as unresolved

Previously, because `mark_new_as_unresolved` was hooked on `save_post`, it would cause edits to fire the action and thus re-change the state to new. This resulted in edits to a post to act as if this was a new post.

This fixes the problem by hooking into post transitions instead.
props @jkudish