Remove the image-only filter and allow all file types to be uploaded

[eykrehbein]

Hey,

I wondered why only images can be selected/uploaded. For some use-cases it may be beneficial to upload other file types, like .pdfs, as well. The function that gets called when any file is dragged into the editor or /image was typed is called insertFiles and is capable of managing other file types as well.
Unfortunately, other file types are excluded in a condition here. Why is that?

Best, Eyk