Harvest: Move ensureTrigger logic outside of component

[y-lohse]

As per #736 (comment), the TriggerManager component still has some logic in it (ensuring an account exists, ensuring a trigger exists, ensuring a folder exists) — it would be good to move this logic. Ideally it would probably go in the harvest helpers, which themselves would eventually move to cozy-doctypes.

[Crash--]

I tried to do it quickly in 4e5a26a but I got so much test erros than I revert it.

I think the best way is to move it directly to cozy-doctypes :)