[FIXED JENKINS-24317] Corrected user dir migration code from JENKINS-23872.
Adapted from #1375 by @daniel-beck: omitting change to User construction, and adding test.
(cherry picked from commit 088edabb31a90cd607f3c6a3123effce5703c817)

Conflicts:
	changelog.html
[FIXED JENKINS-24316] Fixed unknown task icon src path construction

(cherry picked from commit 286337ea39c0db6e056af61e616736bafc5f0581)
Readd static resource path for task icons [JENKINS-24316]

Missed this in previous commit - bad idea making even small changes late at night ;)

(cherry picked from commit 3daa6a97b02635d672e7646e83edb93abf50db06)
[maven-release-plugin] prepare release jenkins-1.577
[maven-release-plugin] prepare for next development iteration
updated changelog for release
updated changelog as a part of the release
merged back the RC branch

Conflicts:
	changelog.html
creating an RC branch
the trunk is toward 1.579-SNAPSHOT
[FIXED JENKINS-21437] Mismatched synchronization monitor.
Better advertising createCrumbedUrl.
Properly documenting the AccessDeniedException as thrown by ItemGroup.read (and methods that call it).
Also making DISCOVER permission be implied by READ, which is natural since it is only checked if READ is denied.