Removing all uses of Zend_Registry from core/ plugins/ and tests/

core/Controller.php

core/ErrorHandler.php

core/ExceptionHandler.php

core/FrontController.php

core/Log.php

core/Piwik.php

core/Tracker.php

core/View.php

plugins/LanguagesManager/Controller.php

plugins/Login/Login.php

plugins/Overlay/API.php

plugins/UsersManager/API.php

tests/PHPUnit/DatabaseTestCase.php

tests/PHPUnit/IntegrationTestCase.php