function getItemById (id) {
        var tmp = null

        angular.forEach(service.files, function (file) {
          if (file.id === id) {
            tmp = file
            return false
          }
        })

        return tmp
      }
Get item from the files array by it's id.

   @param  {Integer}  id  The id of the file (which is actually
                          Date().getTime())