Add example for folder and document listing
Add example for folder and document listing

Summary:
An example how to get the children of a CMIS folder.
The examples creates an output that shows the tree structure
of the CMIS root folder.

Test Plan:
Add a example configuration file and run
`php examples/ListFoldersAndFiles.php`

This should give you an output like:
```
+ [ROOT FOLDER]: Company Home
 + [FOLDER]: My First Folder
   - [DOCUMENT]: My First Document
   - [DOCUMENT]: My Second Document
   + [FOLDER]: My First Sub-Folder
     - [DOCUMENT]: My First Sub-Folder Document
```

Reviewers: claus.due

Reviewed By: claus.due

Subscribers: dkd-dobberkau

Differential Revision: https://phabricator.dkd.de/D2020

dkd/php-cmis-client