Put back the dots before timestamps in discussions (and also remove "commented")

The following discussion from !22333 (merged) should be addressed:

@annabeldunstone started a discussion: (+1 comment)

@fatihacet For diffs, can we revert back to using the dot in between the username and timestamp instead of commented? I think it takes up too much space. I know it was in the designs, so if it's a big effort we can just open a separate issue to look at it later

Edited Nov 30, 2018 by Victor Wu