config: Avoid copying _license_manager

config: Avoid copying _license_manager

Strictly speaking _license_manager is not immutable. Users need to ensure that
extract_global_changes() is called right after __init__ (if at all).
It also has the mutable member _undef_lic_groups. It is used to track
undifiend license groups, to not display an error message for the same
group again and again. Because of this, it's useful to share it between
all LicenseManager instances.