Revamp Achievement system

[chrisj1]

Instead of making each achievement a boolean on the player object I propose we do the following:
Have a dictionary that maps from the name of the achievement to a function that returns if the achievement has been unlocked. This would make adding additional achievements easy and avoid needing to store extra data in the player object.

[tardisfromtornspace]

Hmmm as long as it improves performance and doesn't suffer a bug I'm ok with this.