Bring drag into folder to Files list view

[flamerohr]

Following on the work done in https://github.com/silverstripe/silverstripe-asset-admin/issues/279

Drag and drop is missing from the list view due to limitations in Griddle. It's possible that we'll need to explore an alternative to that library, or maybe revisit it when we are building GridField?

[mister-todd]

Not needed when batch moving files story is completed.

[chillu]

I think with drag/drop moving in the gallery view, and the batch move currently implemented through https://github.com/silverstripe/silverstripe-asset-admin/issues/578, the priority of this decreases - removing from milestone.

[chillu]

@clarkepaul Actually do you think we need to do this at all, given there's two other ways of achieving this goal for the user already?

[clarkepaul]

Hard to say without user testing list view. When user testing drag-drop in the thumb view about half of the users wanted to use drag-drop to move files to their new location as opposed to using the dropdown (so relatively high usage). I think we should have it, it feels like this type of interaction should be a given in a UI like this, although it's not high priority due to having other ways to move items.

FYI I've re-named this issue to "drag to folder" as it could easily be confused with dragging items to a new display order.