properly display thread context for lemmy posts (and perhaps group them together to be less noisy)

**Is your feature request related to a problem? Please describe.**
If you follow a community in Lemmy (see #314 for how to follow a lemmy group), not only will every single post show up in your timeline (which is good)...


But also every single comment to every single post will show up in a way that's completely out of context (which is bad):


Phanpy at least shows that those two are from the Selfhosted group, but doesn't show what post it's responding to or any other context for the messages unless you click on it:


**Describe the solution you'd like**

It would be nice if, at the very least, Phanpy shows that it's part of a thread (with the original group post at the top, and then the thread of responses below that) the same way that normal mastodon toots in a thread are displayed. Ideally, if there are multiple responses at the same time, they are grouped together in the thread so that a user's timeline isn't overwhelmed.

**Describe alternatives you've considered**
An even better option might be for the group to be displayed horizontally, similar to the boosts carousel. I don't know how feasible that is, but especially for a busy community (try @selfhosted@lemmy.world for example) it would be nice. Alternatively, _only_ show the original group post in the timeline, and then click on it to view responses.

**Additional context**
Related to #860 , this would improve lemmy integration. I haven't seen any truly active kbin or similar communities, so I haven't looked into how phanpy integrates with those.

Start by reviewing the existing Lemmy integration referenced by #314 and the related issue #860. Compare how Lemmy posts and comments currently appear in the timeline, then define the chosen grouping and context behavior; done means responses show their originating post or thread without overwhelming the timeline.

Written by the indexing model from the issue text.