ENYO-2674: globally de-activate Dropbox support

…until it is re-tested & re-fixed.

Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>
Merge pull request #475 from enyojs/ENYO-2674

ENYO-2674: globally de-activate Dropbox support