[FIXED JENKINS-3107] Annotate the 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. 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.

2. Currently only handles text-based fields and checkboxes; support for pulldowns etc. TBD.