title: Adding custom parameter in vue2-dropzone event
body: <p>I'm using <a href="https://rowanwins.github.io/vue-dropzone/docs/dist" rel="nofollow noreferrer">vue2-dropzone</a> which exposes a list of <a href="https://rowanwins.github.io/vue-dropzone/docs/dist/#/events" rel="nofollow noreferrer">events</a> E.g. For when the file transfer is complete.</p>
  
  <p>In my SFC (single file component), I use 2 of these dropzone components to differentiate different uploads. I use the event</p>
  
  <pre><code>vdropzone-upload-progress(file, progress, bytesSent)
  </code></pre>
  
  <p>to display progress for each dropzone separately outside the dropzone.</p>
  
  <pre><code>&lt;vue-dropzone @vdropzone-upload-progress="progress($event, 'from_dz1')" ref="myVueDropzone" id="dz1" :options="dropzoneOptions"&gt;&lt;/vue-dropzone&gt;
  &lt;vue-dropzone @vdropzone-upload-progress="progress($event, 'from_dz2')" ref="myVueDropzone" id="dz2" :options="dropzoneOptions"&gt;&lt;/vue-dropzone&gt;
  </code></pre>
  
  <p>When I do that, in my <code>progress</code> method I am only able to get the <code>file</code> object and my custom parameter <code>from_dz1</code> and <code>from_dz2</code> because it matches the first position of the original.</p>
  
  <p>Is there anyway I can do <code>@vdropzone-upload-progress="progress(file, progress, bytesSent, 'from_dz1')"</code> and in my <code>progress</code> method, I do</p>
  
  <pre><code>progress: function (file, progress, bytesSent, origin) {
    console.log(file.name, 'from', origin, progress, '% done')
  }
  </code></pre>
  
  <p>and be able to get all 4 arguments?</p>
  
  <p>A workaround I thought of was to have 3 methods, progress, progress1, and progress2 where both progress1 and 2 would call progress with the additional 'from_dz1' string but it doesn't seem like a scalable idea. If I used more than 1 event I'll end up with many more methods and likewise if I have more dropzones I'll end up with even more methods.</p>