Add a way to display the graveyard

[jleclanche]

There should be a skull-like graveyard button near where the name of the player is right now. Clicking it would display the graveyard as a popup list of cards over the rest of the board state, graying out the rest of the game (like how the sidebar hovers work in hearthstone).

[Patashu]

Worth noting that the concepts of graveyard/died this game are orthogonal (for example, a discarded card is gy but didn't die, and malorne dying leaves your gy but is still resurrectable). Later this might come up as a pedagogical problem (people mispredicting cards like ress/anyfin by looking at the gy and thinking it's a list of dead minions), so something to think about.

[jleclanche]

I think it's possible to clarify that by further displaying the relevant LAST_AFFECTED_BY card (therefore essentially how it died). We can play around with that.