Added NameTag trait for actors

Trait displays the player's name above the tagged actor.

Trait also truncates names that reach a maximum length (this is configurable).

Tested with shroud / fog / cloak / deaths / pixel doubling

![Screenshot](https://f.cloud.github.com/assets/566742/1820651/82f41300-70fc-11e3-8cf4-659aa50880dd.png)