Fix #9

- Compatibility with DataTables 1.10 and FixedHeader

- DataTables 1.10: Need to use anCells rather than _anHidden for the
  cell node reordering.

- FixedHeader: Add a `data-column-index` property to the header cells,
  so we know what column index is being used, even when clicking on the
  cloned cells. This means FixedHeader _must_ be initalised after
  ColReorder - but that was already the case.

- Remove hook into FixedHeader - FixedHeader will now listen for the
  `column-reorder` event and take the required action.