Adding Filesystem class which contains file operations

core/AssetManager.php

core/CacheFile.php

core/Common.php

core/Filesystem.php

core/Http.php

core/Log.php

core/Piwik.php

core/PluginsManager.php

core/ReportRenderer/Pdf.php

core/Session.php

core/Translate.php

core/Translate/Writer.php

core/Updates/0.2.10.php

core/Updates/0.6.2.php

js/index.php

plugins/API/API.php

plugins/CorePluginsAdmin/Controller.php

plugins/CorePluginsAdmin/PluginInstaller.php

plugins/CoreUpdater/Controller.php

plugins/ImageGraph/API.php