Add a notification when DirectEdit starts the download of a file

Currently, when direct editing a file with a big size, there is no feedbacks on the process start, only the opening and the eventual auto-lock of the file.

Nuxeo Drive could, at the beginning of the download of the file on the local machine, give the following notification :

Title : "Opening from [Name of the server]"
Content : "[name of the file.file] is being opened locally"

With this message, the user would understand the fact that the process started, and if an eventual error occurs, would know that it happened before.