ENYO-2514: add an enyo.Signal object to let the event "plugin.phonegap.buildCanceled" fired by the cancel button in Ares.js activate the function abortAjaxRequest() in Build.js.
ENYO-2514: implement the abortAjaxRequest function.

This function is initialize inside each function representing a build step (build waterfall).
ENYO-2514: update the display of the wait Pop-up.
ENYO-2514: Fix an identiation.
ENYO-2514: Fix JsHint warnings.