The 'banned_upload_extensions' array was exactly what I was looking for and worked great, thank you.
The link address when I select an item using "Browse Server", however, is still the same. I have attached a screen capture with the extra path highlighted. The upload folder relative to the website root is "pageAdmin/files". "pageAdmin" is the powerCMS folder. When I truncate the path in the ckeditor to "/pageAdmin/files/1.jpg" it works fine.