LP1683385 AngJS grid avoid dupe auto-fields

LP1683385 AngJS grid avoid dupe auto-fields

When generating grid fields from an IDL class in the AngJS grid, avoid
adding any fields that match fields already defined in the markup.

An example of such a grid is the Pending Item Buckets page.

To test
-------
[1] Go to Item Buckets and add an item to the Pending Items page.
[2] Note that in the column picker there are two barcode fields,
    one that hyperlinks the item and one that does not.
[3] Apply the patch and repeat steps 1-2.
[4] This time, there is only one barcode column (the one that
    hyperlinks the results).

Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>