Add the ability to use custom dice

[LordScree]

The main issue with this option is that it would break some of the dice logic (search code for //TODO). Dice logic currently assumes there is only one of each die, whereas there's no reason in theory why the "?" die couldn't appear twice in the pool.

This might be a case of re-labelling dice as 1...N instead of by their current labels.

Definitely a v2 thing.