Added Created Date, and Author

- show.html.twig >> Moved the "Created on: <datetime>" below the article header, and added a break between it and the article body.
- Blog.php >> Added 2 functions, __construct and setUpdated. __construct writes the current time as created and updated times for the post, and setUpdated writes the current time as the updated time (overwriting the already existing one.)

Signed-off-by: Parth Sarin <parthsarin@gmail.com>