Updated character sprite

Changed main character sprite to use invisible background, 32x32 format
(easier for printing to screen in terms of referencing position in terms
of tiles) and moved to data folder. Wahoo!
Tile Image Changes

Tiles may now change images when 'interacted' with by manipulating
TileID numbers. Added several TODO comments to help prioritise project.
Moved some code around to better areas (calculating things in rendering
now restricted/moved to 'update' method  - shouldn't make a difference
to running speed, just makes it easier to read).