Merge styles from "advgb-styles-renderer"

[htmgarcia]

Styles from post and each block in widgets area are separated.Let's merge into one.
Check groupStylesTag() method.

[htmgarcia]

Moving this to a new milestone in hope we can have more documentation about getting the get_the_content() equivalent for Widgets.

[htmgarcia]

The solution would involve to check all the blocks content in all the widget areas at once, however each block instance in each widget area generates a style tag, plus the one in post content.