JSON validation should fail when multiple rows have same title

[benkeen]

Minor, but still invalid & should be caught. Note that this doesn't apply to all Export Types. With XML, for example, it's perfectly valid.

[benkeen]

This requires an enhancement of the core script.

Right now the Export Types do the job of validating the title field via the validateTitleField callback (ETValidateTitleField interface). In order to accommodate this, that method will need to be updated to pass in all row titles, plus the index of the current row. That would enable it to show an appropriate error + notify the user about which rows were in conflict.