Enlarge and move Jenkins head icon

Enlarge and move Jenkins head image a bit to be flush with the bottom of
the header bar.
Refactor CSS (top > bottom align)

Refactor CSS to make header images relative to the bottom of the header
bar rather than relative to the top.
Merge remote-tracking branch 'upstream/master'
[FIXED JENKINS-19764] Ensure parent dir of new builds dir exists.
[FIXED JENKINS-6153] Add description for label atoms

The change to descriptionForm.jelly is necessary because JEXL
interprets the previous version as a call to the static method
get(String) of LabelAtom if ${it} is of that type.
[JENKINS-6153] Only show configure link for label atoms
[JENKINS-6153] Move @since comment to getter
Incorrect link to master node on label page
typos
use a Builder to create ConsistentHash<Node> 
invoking add(Node, replica) for all nodes rebuild the internal Table many times. Using a builder, Table is only created (and sorted) once
also avoid creating a fresh new Hash object (java 8 lambdas, I miss you)
[FIXED JENKINS-24407] Restore icon class name during deserialization
Merge pull request #1390 from dominiquebrice/incorrect_master_link

Incorrect link to master node on label page
Revisiting 9b7b1364c0f33bb7485ace9b49a6d964e9e9faf9 a bit.

Since ConsistentHash is written as a mutable class, I think a better way to fit the existing design is to provide a bulk add operation.
It already has several methods to that end, so I just added one more that's needed for our purpose.
Noting 990a84
Merge pull request #1377 from daniel-beck/JENKINS-19764

[FIXED JENKINS-19764] Ensure parent dir of new builds dir exists.
Noting #1377
Merge pull request #1380 from daniel-beck/JENKINS-6153

[FIXED JENKINS-6153] Add description for label atoms
Inserted missing at-since
Noting #1380
[maven-release-plugin] prepare release jenkins-1.579