Make datepickers not share options

Calling `.datetimepicker()` on a list of elements causes them to share
options, which causes issues when using data attributes to configure
datetime pickers, as pickers will get the options of the datepickers
before them in the document.

Author: NickBeeuwsaert

src/js/bootstrap-datetimepicker.js

@@ -2402,11 +2402,12 @@
 
         if (typeof options === 'object') {
             return this.each(function () {
-                var $this = $(this);
+                var $this = $(this),
+                    _options;
                 if (!$this.data('DateTimePicker')) {
                     // create a private copy of the defaults object
-                    options = $.extend(true, {}, $.fn.datetimepicker.defaults, options);
-                    $this.data('DateTimePicker', dateTimePicker($this, options));
+                    _options = $.extend(true, {}, $.fn.datetimepicker.defaults, options);
+                    $this.data('DateTimePicker', dateTimePicker($this, _options));
                 }
             });
         } else if (typeof options === 'string') {