Feat: Thread Lines

[cyrneko]

Is your feature request related to a problem? Please describe.

It is incredibly hard to make out in what relations posts are to one another when viewing a post. Reading a thread or looking at replies can be difficult.

Describe the solution you'd like

Introduce Thread Lines.

Thread lines are useful indicator lines that most commonly come down from a root post and continue connecting until a chain of replies ends. They are seen in for example the Web UI or Tusky:

Describe alternatives you've considered

Apart from using another client, you can get small context hints when enabling post dividers. These aren't perfect however and require more thinking. It's less visual than thread lines.