Edited replies are not displayed as replies

[KitsuneRal]

The below either requires using another client that is capable of replying and editing already, or checking out the code from #848. This is not a problem in #848; edited replies made in other clients are shown equally incorrectly.
To reproduce:

1. Make a reply to another message (i.e. make a message event with m.relates_to::m.in_reply_to subobject in its content).
2. Edit this reply and send it.
3. Find the edited reply in Quaternion's timeline.

ER: the message is displayed as a reply and also annotated with "(edited)".

AR: the message is annotated as edited but is no more a reply.

[KitsuneRal]

...and this happens because the edit intentionally removes reply fallbacks. It's time to stop relying on those, generally.