Separate icon for each shader on gnome-shell top bar

[Asif Ali Rizvan]

As a visual indicator to the active shader in use, please have icons at topbar in place of GLSL text for each shader, for example, (just a hint)

luminosity - a light bulb
magnifying glass for magnifier shader
Negative icon for invertcolors
mousepointer with crosshairs for mousetracker
color flower for pixelColorization

Thanks.

[Erwan Douaille]

Commit 17ae2a8 not set in master branch. Not sure if it's a good idea.

You can test with magnifier, mouseTracker, pixelColoration.