Quest engine

Quest engine, at every building placed, will check if that action constitutes the completion of a quest.

When the client detects a change between it's internal quest state and the one it just got from the server, it will alert the player with a message. (you have just completed quest X)

Quests can be configured with a json file, like so:
![image](https://f.cloud.github.com/assets/985892/2351617/955ca71c-a57e-11e3-9d5d-bc998accbcca.png)