0.8.6: :bug: Fix handling of unions of package extras (#97)

* :test_tube: Add failing test

* :bug: Account for extras in Constraint.allows_all

* :bug: Fix tree rendering issue from extras union

* :bug: Fix first come first serve for pin rendering

* :recycle: Simplify bug fix

* :bug: Fix call by reference bleed

* :bug: Handle new extras after package already had a decision

$ pipgrip -vvv smart-open==6.1.0 pypicloud[azure-blob]~=1.3.9