Discover "delegation" in attributes management

[ndeloof]

Some attributes are owned by Jenkins root class for legacy reasons but managed from a web UI point of view using GlobalConfiguration implementation (typically : security has a dedicated page).
We'd like to be able to discover this from the java codebase so we can mimic in the yaml model, so

jenkins:
  securityRealm: ...

would become :

jenkins:
  security:
     securityRealm:  ...

[ewelinawilkosz]

Issue discussed at post-FOSDEM hackathon with conclusion:
ND: "we can do it as Configurator, but if we can do it declaratively we don’t need to keep up with changes in the core"
@ndeloof to attempt to define a core annotation to mark properties, but we anticipate it might raise questions. If that becomes too much pain, we’ll just hard-code those in JenkinsConfigurator

[ndeloof]

#58