Update style.js to treat blockquotes as objects.

Hi,

Blockquotes are broken as inline elements and don't work how I'd expect as a block element but the object element category fits perfectly.

Once correctly set as an object element, you can have paragraphs inside the blockquote and pressing "enter" creates a new <p> tag rather than a new <blockquote> tag.

Also, this allows us to define a blockquote level style.

This appears to have been a previously identified issue here - http://dev.ckeditor.com/ticket/1009 - and I'm having the exact same problem as mentioned there.
Changelog entry.
Merge branch 't/10091'