Add an option to create folders (of both types)

The app should be capable of creation of new folders, be it _root_ or _favorite_.

One of potential implementations is just adding `new folder` button in folder picker.
If the folder picker is inside of a root, then _favorite_ is being created; otherwise — _root_.

Start at the folder picker entry point and trace how the current root and favorite folder types are represented. Add a way to create a new folder from the picker, using its location to choose the type, and verify that both root and favorite folders can be created successfully.

Written by the indexing model from the issue text.