FilePicker: Pin folders from classical view into "Roots" tab

[kirillt]

Context:

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

When the user walks through folders using classical mode, they can pin a folder to the "Roots" tab.

If this folder isn't contained in any root folder:

1. It becomes new root folder.
2. It should be added into global roots file.
3. The .ark subfolder must be created in it.
4. Ensure that "Roots" tab is visible and contains the pinned folder.

If the folder is already contained in an other root:

1. It must be marked as favorite by writing to root-level file listing favorites.
2. Ensure that "Roots" tab is visible and contains the pinned folder.