support drag and drop out of the DM sublist

[ara4n]

No description provided.

[ara4n]

this should be easy to do, and no particular reason not to do it.
When you go the other way (i.e. into the DM list) we should prompt for the target of the DM.

[uhoreg]

Probably not worth creating another issue for this, so I'm leaving it as a comment here since it's related: as noted at https://matrix.to/#/!DgvjtOljKujDBrxyHk:matrix.org/$14855249871111514zbTKJ:matrix.org, dragging a room that's marked as "Direct Chat" from "Favourites" to "Rooms" makes it appear in "People" instead. It should probably un-mark the room as "Direct Chat" so that it it will appear in "Rooms".

[turt2live]

Closing in favour of #8614