ENYO-1740, ENYO-1888: fsDropbox behind corporate proxy (6/5)

- fix fsDropbox.js without a corporate proxy

Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>
ENYO-1740: refine fsDropbox usage instructions

Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>
ENYO-1740: Dropbox: enyo.Ajax#cacheBust

- This is one of _How did this ever work for me before?_

Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>