Reset file upload field when user navigates back

**Problem**

The file upload form submit automatically whenever the name of the selected file
changes.

If the user picks a file, and then navigates back the field is pre-filled
because the page is loaded from the browser’s back/forward cache.

This means that if they pick the same file again, the value of the upload field
hasn’t changed, and the form won’t be submitted.

**Solution**

The solution is to clear the form field[1] if the page is being loaded from the
back/forward cache. Then any time the user picks a file it represents and
actual change.

1. http://stackoverflow.com/questions/8861181/clear-all-fields-in-a-form-upon-going-back-with-browser-back-button

app/assets/javascripts/fileUpload.js

@@ -11,6 +11,9 @@
 
       $form = $(component);
 
+      // Clear the form if the user navigates back to the page
+      $(window).on("pageshow", () => $form[0].reset());
+
       // Need to put the event on the container, not the input for it to work properly
       $form.on('change', '.file-upload-field', this.submit);