[FIXED JENKINS-3107] Expand an Advanced section if some fields are already customized

See [JENKINS-3107](https://issues.jenkins-ci.org/browse/JENKINS-3107). Enough to supersede https://github.com/jenkinsci/ant-plugin/pull/5. Known issues:

1. `advanced.jelly` runs its body twice, once to check for customizations, the second time to actually render. Would be nicer to capture the output and then regurgitate it, but I was not sure how to do this from Jelly.

2. Unclear if `default` comparison logic suffices even for exotic forms. Checked at least on port field for SSH launcher: correctly expands area iff port != 22.

3. So far only handles text fields. Should also handle checkboxes and pulldowns of various kinds.