Implemented ScrollBar limits

-Lists can now only be scrolled so that the top/bottom element is fully
visible

Implementation
-Added FindTopItem() and FindBottomItem as pure virtual methods in List
-Implemented these functions in ConfigList and MenuList
-Added CanScrollUp() and CanScrollUp() in List which uses the above
methods to check whether the top item is ust below the top of the list
area and vice versa for the bottom item
-Added GetBottom() and GetTop() in MenuItem
-Fixed bug in MenuList caused by using List::GetTop() instead of
List::GetItemsTop() which cuased all the items to be added in the same
place
Fixed segfault when no server is present

How to reproduce
-Start a client without the server
-Create a new muliplayer game
-Will throw a segfault

Fix
-Added return false if OpenConnectionToHost() fails

Note
-Not extensively tested, but the bug is fixed and twoplayer still works
normally.
Added different color per line in Lists

-Added functions for calculating the rect of the List item
-Added Item color 1 and item color 2 in MenuList
-Added background color in MenuItem
-Added Item count to List
-Added RenderTools::RenderItemBackground() that takes a ConfigItem and
renders the background of it.
-Changed adding of items in ConfigList
	-Increment item count
	-Set background color in item depending om item count % 2
	-This means every odd numbered item ( 1, 3, 5, 7, ... ) will
	have color 1 and the others color 2
	-Item count is increented before setting color to avoid 0 % 2
	-MenuList will need to be extended before with these changes
	as well for it to work for MenuList