Feature Request: download room history

[The "Migrate your existing Matrix account" tool](https://ems.element.io/tools/matrix-migration) does quite a good job in transfering your account to a new home server including setting roles and parting the old account, which is quite cool. It does *not* transfer the history though, which is totally plausible from a technical point of view.

Though when migrating to a new home server, leaving years of chat history behind might be a show stopper from finally moving away from matrix.org (which is the case for myself by now). The built-in history download thing from inside Element Web is fine for one or two iterations, but it gets sort of tedious when you have a three-digit number of rooms and dms in your account.

So I was looking for a scriptable solution and found `matrix-commander` having candidate potential. Unfortunately, it does not seem to be able to download a room's history yet, does it? So this is a request for a "download room history" feature.