Queue#maintain() was returning too soon

- Added check if running on windows to copy the web dir of the
  WebAppContext

icons after build completion.

Fix for [JENKINS-13195]

Adjust z-index for #search-box-completion to appear over the breadcrumb

Applied the change from Olav Reinert.

Make sure that we don't require Jenkins.getInstance() on CLICommand, since it can run on slaves.

JENKINS-13185: Fix Computer.getHostName() to return the host.name value from the slave rather than null

Fix for JENKINS-13185: If there is a fallback host.name specified, it should return that and not null.