Allow to change Colors and Opacity for Fog of war

[Mephiztopheles]

Currently the fog of war material seems to be very static We can't easily change the color and opacity of each visibility stage

[Mephiztopheles]

This would also be included in #195 The only thing I'm still confused about is that the material doesn't work with the alpha value included. I have to mask all the colors to remove the alpha otherwise we can't apply the color but only a fade to black