Add button to access the Great Vault window? #52

I was thinking this might be a great addition to this addon. It would allow you to open the Great Vault window anywhere in-game. Would save us from having to create a new macro just for it too as it would be built into the addon itself. More info on this Wowhead link.

https://www.wowhead.com/news=319888/great-vault-macro-addon-claim-powerful-gear-and-legendary-powers-with-the-weekly