Fill color

[Rdornier]

I added here the possibility to fill ROIs with a color, with a different opacity.
Everything seesm to work well, except one thing within the small GUI.

1. Select one color for the stroke color
2. Select a different one for the fill color
3. When you click to draw the shape, the radio button changes automatically to match the exact same color in the GUI, but the two different colors have been taken into account for the drawing.

It does not affect the core functionnality but it is annyoing to have a GUI different from what it is drawn. I don't know what exactly happen and couldn't find any fix for now.

Edit: It is related to this issue ome/omero-figure#485

[will-moore]

Working well, with the fixes above.
I wonder if you could also add this to the index.html <style> block, since it's easier to see what's going on with a black background to the canvas:

			#shapesCanvas {
				background-color: black;
			}

[Rdornier]

Thanks for your review.
I fixed the bugs and added the black background.

[will-moore]

Great, thanks!