Only show the publish date in largo_byline() output; move updated date atop the post content

[benlk]

Changes

• in Largo_Byline class and its extenders, remove the case where the post edited time would show
• create new function largo_edited_date() to show the edited date for a post, and allow it to be used outside The Loop
• create action largo_after_hero_largo_edited_date hooked on largo_after_hero that outputs largo_edited_date() wrapped in a div.entry-content.clearfix
• stubbed tests.

Here's how it looks in Largo, and how it interacts with something else hooked on largo_after_hero:

Adopting child theme styles on the site that requested this:

For #1341

[aschweigert]

i think we'll probably want some better default styles here (for the updated date/time) but otherwise this looks good to me, passing off to @Julia67 for a look at the default styles