Move OC_Log_xx to \OC\Log namespace

core/Command/Log/Manage.php

lib/private/Log.php

lib/private/Server.php

lib/private/log/errorlog.php

lib/private/log/owncloud.php

lib/private/log/syslog.php

settings/Controller/LogSettingsController.php

tests/lib/log/owncloud.php