Increase contrast between identicons and background

Identicons currently have a dark or light background depending on the V component of the foreground colour. But V isn't a great measure of brightness - cyan looks much brighter than blue with the same V, for example. This leads to some identicons having low contrast between the foreground and background.

This patch scales the R, G and B components of the foreground colour to 3/4 of the full range and sets the background to white, so there's always good contrast between the foreground and background. The patch also adds a 1dp outline around identicons and adds some padding to the identity selection dropdown.

Before:

After: