Renders editable page content, based on the content_type.

Available content types:

• html: WYSIWYG editor, standard HTML output (sanitized)
• raw_html: Edit the HTML directly, not sanitized -- use carefully
• text: Raw text, all HTML is escaped, basic contenteditable
• image: Displays an image, can edit the URL and alt tag
• background_image: Displays an image as a background image on a div, can edit the URL