Created Purchase and HistoryTableModel classes. Fiddled with HistoryTab
class. In short, added infrastructure for the history tab. Currently as
a placeholder it displays warehouse contents.
Some minor changes
Implemented order saving. Implemented order displaying in the history
tab.
Implemented proper Id assigning to stored orders. Created a listener for
the history table. Now a blank window appears when the user clicks on an
order.
Order details window now displays order details.
Fixed negative quantities in the shopping cart.
Eclipse seemed to think log4j.dtd and log4j.xml files were corrupted.
Uncorrupted them.
Fixed a bug that allowed the payment amount to be changed after
attempting to pay.
Fixed bug - now warehouse quantity is reduced only if the confirm button
is pressed.
Merge branch 'masterbranch' of https://github.com/lauri0/POS.git into
HEAD

Conflicts:
	POS/src/ee/ut/math/tvt/salessystem/ui/tabs/PurchaseTab.java