Fix appearance of bullets/numbered lists (the first level is slightly
indented to the right instead of right on the margin).
New golden files have been tested using Word 2010 on Windows 10.
If the first element of a bulleted or ordered list is another list,
then that first item will disappear if the target format is docx. This
changes the docx writer so that it prepends an empty string for those
cases. With this, no items will disappear.
Closes#5948.