When defining a dashboard group, allow specifying multiple
variables as input to the group meter's LED.  The LED is active
when any of the specified variables evaluates to TRUE, and its
color is the combination of the active variable colors.

Remove the swap-busy variable, and use swap-reading and
swap-writing as inputs to the swap group's LED instead, so that the
LED's color indicates whether the swap is currently being read-
from, written-to, or both.