Added new class to handle adding items to stock.
Updated the stock tab  to display said class and purchase item panel as well (not updating properly though) .
Merge branch 'master' of https://github.com/AtsK/KAT_prj

Conflicts:
	POS/src/ee/ut/math/tvt/salessystem/ui/panels/PurchaseItemPanel.java
	POS/src/ee/ut/math/tvt/salessystem/ui/tabs/StockTab.java