Big modifications on Grid

Change placement of entity on the grid:
	-depending on column and row, not on position.
	-entities are aligned with the columns and rows.

Add a 'topographic' layer to the grid:
	-1: valid placement, 0: unautorized placement

Change the way the grid is displayed on screen.
Correction of the curseur (now gives correct position on screen)

Addition of few entries in the TODO list.
Merge branch 'master' of https://github.com/yohanrodriguez/KingdomWarTD