Imperial article updates

I've done some smaller revisions to older articles, bringing the following articles up to date:

• Quasar article cleaned up a bit, builds updated, and includes discussion on new wave 7 officer options.
• Tarkin article updated to note interaction with Sovereign title.
• Annulling Avenger Boarding Troopers article updated to include Bail and Pryce as counter-options as well as a mention of Captain Brunson.