Steam icons

[pestridge]

New icons for Steam added in 25, 50 and 80px sizes.

[hellcp]

Those don't really conform with the pebble style, having a lot of black filled areas, and the octagons with their low radius don't approximate circles very well as is.

[lavglaab]

seconded- Pebble icons usually use black for stroke only, and white for fill. Here's my thoughts:

• Drop the outer circle from the 25px and 50px variants, and focus on the shape of the piston/hinge assembly
• Redraw all three sizes to create the shape using black outlines (see style-guide.md for reference) and white as the fill color