Use ref-id for all trs

Selection (and sorting) will need to know the ID or reference of the item rather than the index in the display.  This is also needed for Virtualization.  This leads down this direction.

The only controversial piece is the usage of $parent in the TableSelection directive.  This was needed since the scope in the table selection is for the table, but selection usage is likely used in the parent (which would include the toolbar)

Fixes #44