update parametric study to check for duplicates

[safeerehman]

closes #228

• Add a method _remove_duplicate_entries that will remove or update any entries in the parametric study
• The method will have a bool parameter overwrite that will keep the either the first or the last duplicate.
• This method will return an integer specifying the number of duplicates removed
• This method will be called from add_inputs and add_summaries
• add_inputs and add_summaries too will now return an integer specifying the number of entries added.