ListView can match now items belonging to nested ItemGroups

Tricky to emulate the actual web interaction including JavaScript window.confirm;
suffices to just call the web method directly.

Using l:confirmationLink instead of AbstractItem/delete.jelly and AbstractProject/wipeOutWorkspace.jelly.

Expanded MockFolder to be a ViewGroup so that it is possible to test views inside folders,
and generally fixed it to service Stapler hierarchies properly so that WebClient-based tests can work.

[FIXED JENKINS-5408] Quoting Issue with JDK Installer with Windows Slave

The reason is that we always determine the job url using
Functions#getRelativeLinkTo, which keeps the view navigation info if it
exists, and can produce an absolute url if required by the context. So
it is no longer needed for the caller to worry about jobBaseUrl.

By default, names are interpreted in relatively to the current item
group, so Label and Computer views no longer need to set useFullName to
true to have correct behaviour.

https://ci.jenkins-ci.org/job/jenkins_main_trunk/2449/testReport/hudson.console/ConsoleAnnotatorTest/testCompletedStatelessLogAnnotation/
junit.framework.AssertionFailedError: expected:<3> but was:<4>
	at junit.framework.Assert.fail(Assert.java:57)
	at junit.framework.Assert.failNotEquals(Assert.java:329)
	at junit.framework.Assert.assertEquals(Assert.java:78)
	at junit.framework.Assert.assertEquals(Assert.java:234)
	at junit.framework.Assert.assertEquals(Assert.java:241)
	at junit.framework.TestCase.assertEquals(TestCase.java:409)
	at hudson.console.ConsoleAnnotatorTest.testCompletedStatelessLogAnnotation(ConsoleAnnotatorTest.java:69)

Conflicts:
	changelog.html

[FIXED JENKINS-15340] Ask for confirmation before reloading config from disk, as it may be expensive.
First of all, /reload should require POST (also prevents XSS DoS attacks).
Adding <l:confirmationLink> to encapsulate a link that requires confirmation upon clicking.
Allowing a ManagementLink to request confirmation (also implying POST); could be used also for e.g. /quietDown.
Enhancing <l:task> to support confirmation as well, and honoring this in context menu items.

Conflicts:
	changelog.html

complete relative url, in order to take into account the current view.

Added some unit tests

The view content needs to be determined by getItems as the content can
change even without view definition modification.

(Not touching the icon since I do not feel like playing with Inkscape; would be a nice pull request for somebody.)

https://github.com/jenkinsci/jenkins/pull/757.