Update to Player's Line of Sight, Enemy Pathfinding

* Player LoS updated to be based on mp_grid tiles instead of pixel
distance
- Player's LoS is refreshed each time it moves to a node on it's path
- An object nodeTracer is created on each node in Player's path;
collision with Player refreshes LoS and destroys the nodeTracer (this
allows for the illusion of "dynamic" LoS since the refresh is done
before the Player has completely entered the tile)
- Bug: Cannot differentiate fog's alpha based on distance (originally
N/E/S/W tiles had 0 alpha and remaining LoS tiles had 0.x but now all
LoS tiles have 0 alpha

* Enemy creates and maintains a rangeArray, an array containing the
mp_grid tiles it can act in - when Player moves within range of the
Enemy, weights are assigned to those tiles which can influence where the
Enemy moves

* Minor graphical bug with grid background fixed (shifted background 1
pixel down so LoS would be viewed better)

* BUG: Player and Enemy still detect each other via pixel distance - fix
in each object's Step events