I 1 comments after emoji

Check last action (comment/commit) on a PR which has an emoji comment to see if the emoji was the last update. If a non-emoji update was last, post the user's avatar and a :speech_balloon: to indicate further activity. This is to prevent the PR view showing a :+1: when further updates have been posted since.

Closes https://github.com/conroyp/thumb-checker/issues/1