Update JNA to 4.1.0.

JNA 4.1.0 has a proper license, so remove workaround in
licenseCompleter.groovy. [JENKINS-24521]
Update libpam4j to 1.8, which uses JNA 4.0
Update memory-monitor to 1.9 which uses JNA 4.1
Documenting what this setting controls
Restored backward compatibility.

Up to b5843f3, <t:ballColorTd> supported @iconSize="16x16" and so on that controls the color.
In the new scheme, it needs to be translated to iconSizeClass
[FIXED JENKINS-24521] Merge branch 'pull-1387'