[FEATURE] implement new feature "listfiles" (content of t3x files)

This feature enables users to list the content (files) of a t3x file, without extracting the files.
New command line argument introduced:

Usage: bin/t3xutils.php listfiles <t3x-file> [details]

By using the optional third argument "details", MD5 hashes and file sizes are included in the output. Without "details", only the list of files is shown.

The phar files has not been changed yet.