Refactored how activity-comment level’s are calculated in the activity adapter

UI counterpart for https://github.com/oaeproject/Hilary/pull/935
This is now showing all comments rather than the latest 2 (+ their parents). Even changing this to `activity.latestComments` doesn't seem to fix the problem in the following case:

- Add top level comment 1
- Add top level comment 2
- Add reply 3 onto comment 1

In that case, the expectation is to see the following in the activity feed:

```
- Comment 1 (as parent of reply 3)
  - Reply 3 (as latest comment)
- Comment 2 (as second latest comment)
```