[client] Support jokers

[joshuaauerbachwatson]

The deck image that I am currently using for the "default source deck" doesn't include any jokers and so I did not make provision for having optional jokers in the playing decks. This could be addressed

• specifically by just finding joker images of the correct shape and incorporating them into the default source deck in code (there is no requirement that the deck be cut from a single image or using any particular pattern)
• more generally by changing the source deck (and at the same time I should consider allowing the source deck to be a user choice)

[joshuaauerbachwatson]

In working on this I found it was easiest to add jokers to the existing source deck (I could not find good source deck images that included jokers). So, I narrowed the scope to just adding jokers, not any additional tailoring.

As separate low priority additional work I think we can separate the following.

1. Support user-defined playing deck templates. This is relatively easy because the templates are compact metadata (don't include any images).
2. Support alternate card graphics (source decks, possibly distinguishing the card back from the fronts). This would be a developer task, by supplying the choices with the game. End users could not add more art to an existing version of the game.
3. Support users ability to add card graphics without downloading a new version of the game. Hard. Probably out of scope for now.