Added sortablelist plugin. It is used to change order of items in listvi...

Make items sortable by drag-drop in list view. Diffierent from builtin plugin sortable, it touches model field indeed intead of only for display.

![idc_list___django_xadmin](https://cloud.githubusercontent.com/assets/1997991/4648338/65a82714-5481-11e4-8e78-cf7f823bd6fe.png)