- removed "populateWithHistoryData()" from HistoryTabModel, as per Anu's suggestion
- modified addItem() mehtod in PurchaseInfoTableModel. Now it checks if item you are adding is already in the currentPurchaseTable and if it is it icreases the quantity.
Also checks if there's enough items in the warehouse to add - if not, throws exception
- PurchaseItemPanel, addItemEventHandler catches that exception and prints log
- some small cleanup