Adding the controller action, UI and associated code for editing posts.

This is, verbatim, the second of three [implementation steps](https://github.com/jdickey/new_poc/issues/52#issuecomment-53987745) expected for getting the post-editing workflow working as per Issue #52.
Place the . on the previous line, together with the method call receiver.<br>Prefer double-quoted strings unless you need single quotes to avoid extra backslashes for escaping.