ENYO-2514: add a new wait Pop-up specific for build action.

It contains and additionnal "Cancel" button to cancel a build.
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.
Merge branch 'master' of github.com:enyojs/ares-project into ENYO-2514
ENYO-2514: removed dead code
ENYO-2514: added comment
ENYO-2514: removed log
ENYO-2514: simplified build phase test
ENYO-2514: document workaroung with a JIRA number
ENYO-2514: work-around xhr abort issue on Mac

On Mac, response is called even if the xhr was aborted.
ENYO-2514: run xhr.abort() at the end of abortAjaxRequest
Merge pull request #644 from enyojs/ENYO-2514

ENYO-2514: Add a button to Wait pop-up to cancel a build request.