Remove the rem mixin - it not needed as the px fallback has been dropped
Make sure visited buttons and menu items are shown as any other button/item
Rename variables

Color changes:
* $color__gray is now #999, not #555
* $color__gray-light is now #ccc, not #999

$color__gray was not used before and #ccc was used 4-5 times so it
makes more sense to have that in a variable.

This commit also reduces the number of different grays used - that
number was way too high.

The accent color variables has been removed. Not many of them were
used, and those who where only 1-2 times.