Added drop-down menu
Edited the drop-down menu: now the other fields are filled when an item
is selected from the menu, not when the drop-down menu loses focus.
Added the "sum" column
Added warning message when the inserted quantity is too high
Warehouse quantity is reduced if item is added to shopping cart - this
must be specified
Added adding to warehouse functionality
Added "Add existing product" button to the warehouse
Merge remote-tracking branch 'origin/HEAD' into HEAD

Conflicts:
	POS/src/ee/ut/math/tvt/electricsheep/Intro.java