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-21881] System property for disabling X-Frame-Options
[JENKINS-21881] Add test
Merge pull request #1360 from sfarbota/master

Enlarge and move Jenkins head icon
Merge pull request #1391 from daniel-beck/JENKINS-21881

[FIXED JENKINS-21881] System property for disabling X-Frame-Options
Noting #1360, #1391
Updated since