Upload and list files: Display and process forms to upload files

This class can be used to Display and process forms to upload files.

It can display an HTML form with fields to upload a file.

The class can also process a form with an uploaded file by checking if the file if of one of the allowed file MIME types name extensions, and moving the file to a given directory if does not exist already.

The class can also create the destination directory with the necessary permissions.