show comments on page load unless dismissed before

[hn3000]

When a page is loaded while lean-in is active (or lean-in is activated on demand) comments that exist for a page (meaning they are attached to the page, not just passages of text) should be actively shown to the user. An option should exist to prevent having the comment show up on the next page load ("don't show this again" checkbox). The activation UI should still show that comments exist for the page.