[FIXED JENKINS-18680] Update members of a ListView using a regular listener, not View.onJobRenamed which does not work with folders.

In /asynchPeople, check progressive rendering cancelation status between each user; UserAvatarResolver could be slow.

Otherwise get e.g.:
java.lang.IllegalArgumentException: java.lang.NullPointerException
	at hudson.model.ItemGroupMixIn.createProject(ItemGroupMixIn.java:253)
	at hudson.model.ItemGroupMixIn.createTopLevelItem(ItemGroupMixIn.java:175)
	at jenkins.model.Jenkins.doCreateItem(Jenkins.java:2827)
	at jenkins.model.Jenkins.doCreateItem(Jenkins.java:308)
	at …
Caused by: java.lang.NullPointerException
	at hudson.model.ItemGroupMixIn.createProject(ItemGroupMixIn.java:251)
	... 65 more

Throw Failure, which FormException would just delegate to when we are not coming from a regular form’s Apply button, as in this case.

Also ensuring that Jenkins configuration is saved after new XML is POSTed.

[FIXED JENKINS-18118] Introduced UserAvatarResolver.resolveOrNull to properly produce fallback icon URL.

Object that implements ModelObjectWithChildren can expose its children in the breadcrumb.

[FIXED JENKINS-16397] Just displaying /asynchPeople constructed the expensive People object merely to decide whether or not to display the “REST API” link.

This change does not necessarily improve total performance, since the avatar is still computed.
But (1) the computation is correctly done in the work thread, not in the HTTP response thread;
(2) the computation is done just once for a given User, which could reduce load when many AJAX checks are done.

Plus fixing the wrong apply button handling in various code.

(Its index.jelly does assume getDisplayName is available.)

From what I was told by Emanuele today in the office hours, this came up
during the Copenhagen hackathon.

Update transient action after config submit, as trantient action may change due to change of view properties.

See https://github.com/jenkinsci/jenkins/pull/474 for the original conversation

The trick for backward compatibility is in the default implementation
that grants View.READ to those who have access to items.