[JENKINS-3107] Expand an Advanced section if some fields are already customized.
Initial implementation handles only text fields, not e.g. checkboxes.
[JENKINS-3107] Rather than preëxpanding the Advanced area, just show an icon.
[JENKINS-3107] IE 9 fix.
[JENKINS-3107] Icon looks better before button rather than after, for reasons of alignment with the rest of the form.
Merge remote-tracking branch 'origin/master' into advanced-auto-expand-JENKINS-3107
customizedFields support for f:checkbox (and thus also f:optionalBlock).
Merge branch 'advanced-auto-expand-JENKINS-3107'
[FIXED JENKINS-3107] Annotate the Advanced section if some fields are already customized.