Allow uploading images through TinyMCE image uploader!

[tadhgboyle]

@Derkades What would be the standard here for returning the error header with the error text? Is what I have now okay?

Couple things to do:

• Show error message in TinyMCE popup, not just "http error 500"
• Token check

Deals with #2170 (can't see any open issues for it?)

[Derkades]

I'd change it to

if (!$upload) {
    http_response_code(500);
    die("Failed to upload image" . $image->getError());
}

and

http_response_code(400); // Bad request
die("No image uploaded");

Your current code tries to set the header "HTTP/1.1 500 Server Error" which doesn't make sense. The status code is sent before the headers in an HTTP response and messages belong in the response body.