Fixed dragable styling for Firefox.
* Switched text-indent from 100% to 100px to move the "D" over so that it
wasn't visible.
* Since position: relative isn't defined for table elements, I added a
  div which can have relative position inside the first column.
* Moved styles out of the #nested-fields scope, because when an element
  is picked up, it is not within #nested-fields and it loses its
  styles.
Merge pull request #380 from sul-dlss/firefox_drag

Fixed dragable styling for Firefox. Fixes #376, Fixes #291