NEXUS-6019: ModelloUtil expanded for configuration stuff

New methods added that completely cover current capabilities
of Nexus configuration "framework", plus, using FileReplacer,
and all in one class.

Used in
https://github.com/sonatype/nexus-pro/commit/55b9ff4473750d7c3b195d467ce9b24c805b5efa

CI
https://bamboo.zion.sonatype.com/browse/NX-OSSF37