Renamed back to "Item" instead of "Arrow"

In order not to confuse anyone, the methods containing the word "Arrow"
were renamed to "Item" (except for those ones marked as deprecated;
these methods will get removed soon).
More tweaking options for rounded borders.

The arc width and height can now be set individually
if rounded borders are being drawn.
Added manual listener triggering.

Commit gives the programmer the opportunity to trigger the listeners
registered with the component himself, adding a bit more flexibility.
Edited arrow selection mechanism.

Inventory:
	- Inventory objects accept now java.lang.Class objects aswell for putting
	  items into the inventory. No instanciation of items needed.
InventoryEntry:
	- Generalized the linked list in which the items are being stored.
ConfirmDialog:
	- Moved to package "gui".
	- Edited listener mechanisms a bit.
ArrowSelectionScreen:
	- Made adding of arrows to the inventory a bit easier.