I added a simple Class for units to work with - the actual Class will be
more involved and may need to be a parent/child approach, but this gives
a bit of content for the tile grid to begin to work with

I updated grid_map to add 5 units and place them randomly, but it doesn't
highlight them when clicked - I need to adjust the logic for that yet

Signed-off-by: TimboDude <pastortim@walloonchurch.com>