Option: Return 1px image

Problem/Motivation

There are times when the tracker needs to return an image.

Steps to reproduce

Proposed resolution

send_image=0 No Content
send_image=1 1 px gif

Remaining tasks

User interface changes

API changes

    $gifData = hex2bin(
      '47494638396101000100800000000000' .
      'FFFFFF21F9040100000000002C00000000' .
      '010001000002024401003B'
    );

    $response = new Response($gifData);
    $response->headers->set('Content-Type', 'image/gif');
    $response->headers->set('Content-Length', strlen($gifData));
    $response->headers->set('Cache-Control', 'no-cache, no-store, must-revalidate');
    $response->headers->set('Pragma', 'no-cache');
    $response->headers->set('Expires', '0');

Data model changes