Add images for composers, conductors and works

[terual]

As requested in #1046 (and added icon for conductors and composers for good measure)

[michaelherger]

Oh wow!... you just qualified as the icon artist! Would you have a template how to create that depth effect? I tried to do this using gimp, but failed...

May I ask you to tweak the "works.png", to give it a bigger margin top/bottom?

[terual]

You mean to reduce the size of the treble clef?

[terual]

I have changed the size of the clef, is it better like this?

BTW, this is all made in Inkscape, so I can share the template svg I made. Do we want to store the template inside of the source tree?

[michaelherger]

Excellent! Yes, please, if you could share the template. Probably on lyrion.org rather than the source repository?

[michaelherger]

BTW: I'd usually send images through ImageOptim (https://imageoptim.com/mac - Mac only), which in turn seems to be using TinyPNG (https://tinypng.com), which easily squeezes out 50% of the image size:

[terual]

...I ran optipng -o7 works.png before commiting. Weird that further optimization is still possible then.