blog: Move the title field to the main column
blog: Move the title field to the main column

This makes the main column more obvious, by reducing the size of the
metadata sidebar.

As a result, the writing workflow should be made more obvious:

* write a title (what the article is about)
* write the article
* optionally write a summary
* eventually, have a look at that small sidebar to see if there's
  anything you need to change in there

Relates to #771

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