[FIX JENKINS-22971] Show full project name when in folder.

Jenkins currently shows the full name of a project on its index page when a display name is set.

It should also show the full name when the parent is not `Jenkins.instance`, i.e. the full name not equal to the project name. Projects frequently need to be referenced by their full name (Copy Artifact, Build other projects, ...).

Full name | Full display name | Full name shown?
--- | --- | ---
foo|foo|No *(same as project name)*
foo|Foo|Yes
bar/baz|bar » baz|Previously no, now **yes**
bar/baz|bar » Baz|Yes
bar/baz|Bar » baz|Previously no, now **yes**
bar/baz|Bar » Baz|Yes