Updates for new Piwik version 2.2.0

* Added custom template for 'visitors by countries'. NB! 'Live visitors
counter' works only if custom template field for 'Visitors by countries'
is empty.
* Fixed an error w/ undefined method Access::isSuperUser
* Fix for double slash in ajax url
* Added workaround for getallheaders() method if PHP running as CGI.
* Remove PIWIK_ENABLE_DISPATCH due to triggering an error while
generating counter image.