[initiative] Initiative Tracker

[oakbrad]

DM should be able to use /init command in a thread or channel and all players will have initiative rolled for them, tracked in a Discord embed with buttons for moving <- -> through the order.

Settings store: the DM role, the player role, and a per-user setting of /initmod to add to their roll.

DM needs some way to add monsters /initnpc [name] [mod] maybe