Feature name column is no longer dimmed

When a single feature row is selected, the other columns' names are no
longer dimmed. Fixes #128.
Obsolete browser columns are partially desaturated

New feature: when "show obsolete browsers" is enabled, the additional
columns are drawn using slightly desaturated colours to offset them
from the current browsers.
Merge pull request #176 from webbedspace/css

Some CSS changes