Display each drive filebrowser in a separate side panel

This PR implements:

a command accessible from the command Palette with label "Add a New Drive Filebrowser" that opens a dialog listing all the available drives (the available S3 buckets are listed in the backend, but here fake buckets with fake content are used instead of using a get request).
in the dialog, by clicking on add drive buttons the user can add a new drive in the table displayed on the right, if the status of this drive is active. If not, a warning is sent. At the same time, a new left sidepanel is added, containing the filebrowser of the drive that has just been added.
By using the contextual menu (right click on the "D" drive icons in the sidepanel), it is possible to remove a filebrowser and dispose the drive, using the command labelled as "Remove Drive File Browser". It uses a logics based on retrieving the id of the panel when the user click on its respective button in the left sidebar.
The logics related to the update of the selected drives is made mainly in driveListManager.tsx, by the specific react components and a VDOMModel that is update at any change.

cc : @afshin, @jtpio

QuantStack / jupyter-drives