Add testcase for nested extra keys

[Baachi]

The RouterVoter requires a litte bit more complex structure in the extra keys, in order to calculate if an item is active or not.

Example:

account_tabs:
    tree:
        admin:
            label: Admin
            route: admin
            extras:
                routes:
                      - pattern: "/^admin/"
        profile:
            label: Profile
            route: profile
            extras:
                routes: 
                    - 'profile_update'
                    - 'profile_index'
                    - 'profile_change_password'

[jbouzekri]

@Baachi : Merged and tagged (7.1). Thank you !

[Baachi]

@jbouzekri Thanks for you work and this bundle!