ENYO-1740, ENYO-1890: implement Hermes verbs on top of dropbox-fs

Next (and last) step is to make this work behind a corporate proxy.

* Merge remote-tracking branch 'enyojs/master' into ENYO-1740 (HEAD, enyojs/ENYO-1740, ENYO-1740)
* ENYO-1740, ENYO-1890: Dropbox, enhance & document GET
* ENYO-1740, ENYO-1890: Dropbox, fix PUT of existing file
* ENYO-1740, ENYO-1890: Dropbox, implement MOVE & COPY
* ENYO-1740: Dropbox, implement DELETE
* ENYO-1740: Dropbox, implement GET
* ENYO-1740: Dropbox, implement PUT (2)
* ENYO-1740: Dropbox, implement PUT
* ENYO-1740: temporary checkin of modified (fixed) dropbox-js
* ENYO-1740: use modified node-XMLHttpRequest from enyojs
* ENYO-1740: remove xmlhttprequest module from dropbox


Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>