grey out text/icons for inactive steps
grey out text/icons for inactive steps

...rather than opacity, which looks odd and cheats by introducing more
colors

[#97774988]

Signed-off-by: Toby Rumans <516e7840355d33b790e9dc5c111fe7c7c270a08f@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse