Cloak grenade gfx : update placeholder and create the colored gfx icon.

Finally, I kept the placeholder design. Maybe I was already used to see it in the scoreboard. 
I changed it a bit to be more thick. The colored gfx is greenish / yellowish to have his own color identity inside the colection of nade. I advice a color like ^xAF0 for the icon in the scoreboard as well.