Fix account switcher requiring two tries on Firefox
Correct handling of cookie deletion with a callback.
support deletion of multiple cookies at once
use $.Deferred for callback after delete cookie in RESUtils.deleteCookie
refactored BrowserStrategy.deleteCookies and BrowserStrategy.deleteCookie from RESUtils.deleteCookie
Merge pull request #1823 from andytuba/1771

use promises when deleting cookies (for account switcher)