Split Sprites file into 'MyGUI' and 'GridManager'.
-GridManager handles info about what the currently selected attributes are and the list of grid cells (tiles).
-MyGUI handles the GUI on the right.
Added Tile object which holds data about each tile.
Added TileHolder object which holds the tiles in each Grid GameObject.

Shift-Clicking will now load the attributes of the tile you shift-click on.

Added parameters for 'Passable' and 'Standable'