Skip parsing item XML if identifier is already present in database

[ryanashcraft]

Description of Issue

Parsing needs to be optimized so that if an item will ultimately not be added to the database, then it won't parse through all of the item's inner elements.

Suggestion

When parsing and started parsing an item XML element, use regular expression search to get Item identifier. Go ahead and determine if that identifier is already in database. If so, then skip parsing that item and set the corresponding copy of Item's keep to YES.