Reformat method visibility according to PSR-2

core/Access.php

core/Archive.php

core/ArchiveProcessing.php

core/CacheFile.php

core/Common.php

core/Config.php

core/Controller.php

core/Cookie.php

core/DataTable.php

core/Date.php

core/FrontController.php

core/HTMLPurifier.php

core/Http.php

core/IP.php