Add possibility to load files from a given directory

[threadi]

Add a way to load and list files from a defined directory on the server instead of from the media database.

• [ ] How to set the title and description of the file if they are not in the media database?
• [ ] Add tab in Media-Choose-Popup to select the directory. Setting is saved on the block.
• [ ] Add button to re-read the directory with a click.
• [ ] Read out and display files in the directory.
• [ ] Possibly make available as a separate plugin that connects to downloadlist, as it would considerably exceed the intended scope of functions.

[threadi]

Better to use already existing plugins for this task.

E.g.: https://wordpress.org/plugins/add-from-server/