Merge Group Chats and Call Logs

[deepspaceaxolotl]

Opening an issue for what was discussed in #50.

Looking through my database, most of the "chats" are actually group calls (Conferences) that generated a new chat every time, so some way to merge all of those into another group chat (Group or Conference) depending on the participants would be excellent (ideally being able to uncheck ones that were intended to be separate group chats, and maybe some way of dealing with merging group chats with names where the named one(s) aren't the earliest created (picking what name to keep, basically)).

Might also need some way to preserve the metadata of who was in the call when it varied (I'd want to merge chats where someone dropped out/didn't answer or was added to the call into the same chat)... Not sure if it could be attached to the call start and end messages, perhaps? Hmm.