Fix tag order when selecting existing tags
Fix tag order when selecting existing tags

refs #5773
- overrides ember-cli-selectize's `_addSelection` method to insert objects at the correct index instead of always adding at the end

airycanon/Ghost-Admin,TryGhost/Ghost-Admin,JohnONolan/Ghost-Admin,dbalders/Ghost-Admin,airycanon/Ghost-Admin,kevinansfield/Ghost-Admin,JohnONolan/Ghost-Admin,acburdine/Ghost-Admin,acburdine/Ghost-Admin,kevinansfield/Ghost-Admin,dbalders/Ghost-Admin,TryGhost/Ghost-Admin