Declare visibility on class property

Checked core and extensions for possible usage. Found no occurrences. Make
protected, so it is accessible when subclassed.

Change-Id: I5f25cbaf20215bce9c9d614c76df906c6b9cba93
Declare visibility on class properties

Set to protected, so they are accessible when subclassed. Grepped core and
a little over 600 extensions for usage. Only usage found in UploadBase.php
and no direct usage of class properties.

Change-Id: Icb3a43867670f140f05643379c7acad34c6518c1