As a user I want to know how many comments are on a post when viewed in the Activity stream

As a user I want to know how many comments are on a post when viewed in the Activity stream. Currently the Topic page shows a nice button indicating the number of Comments that are on a Post, but there is no number of comments for posts when shown on the Home page or Group Activity Streams.

Note: in Commons 6.x-2.x had the number of comments so I've added this to #1930406: [Meta] - As a site Administrator I would like to upgrade from 6.x-2.x to 7.x-3.? without losing functionality.