Improve contrast of app icons

[kra-mo]

We heard feedback that it was too difficult to disambiguate icons in the new menu. To be able to more easily tell icons apart from each other, we should flip the colors:

• The foreground color should be derived from primary
• The background gradient from secondary
• The shadow and top shine should be removed
• And we can also slightly increase the size of icons and the circles they're in

cc @pringelmann @jancborchardt

[kra-mo]

Also, please tell me if the foreground color for the icons is only achievable with some funky CSS filters and complicated logic. If it would be too complicated… I can settle for plain black with an opacity gradient :)

[kra-mo]

Actually, mask-image is probably a better idea

[pringelmann]

We may need to change the hover color to something else:

Any ideas? I can try a few variations and share screenshots

[kra-mo]

Could maybe just make the circles grow a little bit on hover? And appropriately shrink when active.