Change wording of reply count

During the design meeting @aron raised the point that additive reply counts are confusing because replies may only be a reply to the reply and not to the top level annotation.  The number is correct but we need to change the wording to not use reply/replies. 

This was discussed in the design meeting but is so trivial I decided to make a Pull Request rather than raise an issue. 

What do people think about comment/comments? It's what Reddit uses.