Improve UI abstractions

[ajps]

Do a better job of abstracting the "game" from the UI used to control it, such that the only things that the "game" cares about are those things that change the game state - which are passed to it in the form of "commands".

See http://rephial.org/wiki/UIAbstraction for more details and evolving plans.

[ajps]

First stages of this were implemented in [522] and [523] some time ago, the latest change which moves the birth process across is in [815].

[ajps]

More implemented in [1364] where a new command passing setup was introduced and birth overhauled again - everything's easier without the autoroller to contend with.

[anonymous]

Yet more in [1417], moving most game commands over to the new system, overhauling the command interface some more.