ENYO-1740, ENYO-1884: switch fsDropbox from manual to `dropbox-js` library

* ENYO-1740, ENYO-1884: switch fsDropbox from manual to `dropbox-js` library
* ENYO-1740: update dropbox-js from 0.3.5 to 0.8.1 (micro-tech/ENYO-1740)
* ENYO-1740: after run of `npm rebuild`

Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>