Removing last Piwik_ occurences

core/Plugin/Visualization.php

core/QuickForm2.php

core/ViewDataTable/RequestConfig.php

plugins/API/API.php

plugins/Actions/Actions.php

plugins/Annotations/Annotations.php

plugins/CoreAdminHome/CoreAdminHome.php

plugins/CoreConsole/CoreConsole.php

plugins/CoreHome/CoreHome.php

plugins/CorePluginsAdmin/CorePluginsAdmin.php

plugins/CoreUpdater/CoreUpdater.php

plugins/CoreVisualizations/CoreVisualizations.php

plugins/CoreVisualizations/JqplotDataGenerator.php

plugins/CustomVariables/CustomVariables.php

plugins/DBStats/DBStats.php

plugins/Dashboard/Dashboard.php

plugins/DevicesDetection/DevicesDetection.php

plugins/ExampleRssWidget/ExampleRssWidget.php

plugins/ExampleUI/ExampleUI.php

plugins/ExampleVisualization/ExampleVisualization.php