Update python-eyed3.spec: add py3-grako weak dep
    
    The grako module only exists in python3 form, in the Fedora repos, but
    since we have access to that, add `python3-grako` as a BuildRequires and
    soft Recommends for `python3-eyeD3`.
    
    Also reenable - in python3 only - the `test_display_plugin.py` test
    which was disabled due to the grako dependency.
    
    https://src.fedoraproject.org/rpms/python-eyed3/pull-request/3