Collect accent blue shades

[fbarl]

The following 4 colors are all of very similar hue and saturation. Moreover, they are used either to highlight a piece of information or to show some info/metric, so they have a lot in common:

hsl(197, 97%, 34%) - turquoise
hsl(197, 96%, 43%) - status.info
hsl(191, 100%, 50%) - accent.blue
hsl(208, 100%, 97%) - aliceBlue

I suggest treating them as different shades of the accent blue color (in line with #262):

hsl(197, 100%, 35%) - blue700
hsl(197, 100%, 45%) - blue600
hsl(197, 100%, 50%) - blue400
hsl(197, 100%, 97%) - blue50

cc @bia