Added concept of different types of backgrounds, as well as boiler-plate
code to get to the 'background picker dialog'. Need to actually finish
said dialog to test background functionality.
Updated resource packs to have backgrounds and patterns for testing. UI
for background selection is not working yet, but background drawing is.
Having considerable difficulty getting the rows of background buttons to
actually scroll; burned through multiple different layout managers and
none seem to properly communicate to the ScrollPane the size of the
panel when the buttons have been added.
Updated debug world with new backgrounds; Background system IS working.
The only issue is that the background picker, for some reason, does not
show scrollbars properly when it should, which limits the number of
potential backgrounds that can be selected.
Added more patterns to make issue of no scroll bars apparent in debug
world even at refined size.

Found a long-standing bug where there could only be a max of 10 (0-9)
types of sprites, backgrounds, or patterns because ArrayList.add (and
LinkedList.add) can't handle adding to a specific index if the size
isn't big enough. I was under the wrong assumption that they did that.
Converted to basic arrays of size 256 for now, but eventually wish to
replace with a class that can handle what I need without a hard-coded
upper bound.
Direderp (Or rather Erika-derp). Added the PANEL to the tabbed pane, not
the SCROLL PANE. 

Removed irrelevant BorderLayout commands since this uses SpringLayout
now.