[Direct Transfer] Add CSV export capability for sessions

User Story

As a user, I want a CSV file of all files and folders transferred during a specific session.
That file can be used later with the CSV importer of the platform.

Scope

• At the app startup, create the csv folder in the app-specific folder.
• Add a new database table: SessionItems. It will contain 2 fields: session_id and data. data will contain the JSON sent by the server at the document creation.
• For each transferred item in a given session, save the JSON data into the database.
• Add a nice "CSV" icon/button on the sessions history.
• Clicking on the button will:
  • Generate the CSV file (see specifications, formatted like "session 2021-02-05 16-52-04.csv"), it will contain:
    • name
    • dc:title
    • type
  • Then open the folder containing CSV files and select the generated file. Note: the capability to select a file is available on macOS and Windows only, see NXDRIVE-848 for GNU/Linux.