Discovery of manually synced ARK folders

[kirillt]

Simple scenario:

1. User syncs or copies manually an ARK-enabled folder from another device.
2. The synced folder should magically appear as featured in ARK mode of the filepicker.

User might already have .ark-roots file in the filesystem.
User might be not aware of what is ARK-enabled folder or if it contains hidden .ark subfolder.
User might have only one app of ARK family, e.g. Retouch or Shelf.