Image Rotator: Pick random file from a directory to display

This class can pick a random file from a directory. Despite it can be used for displaying rotating banner images, it can be used to randomly pick an other type of file.

The class can traverse a given directory to retrieve all files of a given list of file name extensions. Then it can pick one file randomly to be returned as the selected file.

Optionally, the starting directory can be traversed recursively. This way the class can return files from sub-directories of the starting directory.