FilePicker: Automatic discovery of ARK-enabled folders

[kirillt]

Context:

• FilePicker: ARK view ("Roots" tab) #51

User may sync or copy manually an ARK-enabled folder from another device. The synced folder should magically appear in "Roots" tab of the filepicker.

User may:

• already have .ark-roots file in the filesystem
• be not aware of what is ARK-enabled folder
• be not aware of hidden .ark subfolders
• have only one app of ARK family, e.g. Retouch or Shelf

How to solve this? Scanning the whole filesystem every time doesn't look reasonable. Is it ok to do it in background?

[kirillt]

Roots scanning was implemented within the scope of this issue:

• Automatic root folders discovery and favorite folders persistence  ARK-Navigator#221