Pull request to add multiple features to cleditor-extimage-plugin

I have added multiple features to the cleditor-extimage-plugin including...
- A standard upload handler script in PHP.
- Error messages in the upload return page.
- Added validations and accompanying error messages in the PHP script.
- A simple paginated listing of image files in the image directory.
- Image select from the paginated list.
- Image delete from the paginated list.

I thought you might want to add some or all of these features and changes.