Added RenderNameTag 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

![nametag2](https://f.cloud.github.com/assets/566742/2190713/41e709fc-9830-11e3-9f20-0039d2f2cafd.png) ![nametags2](https://f.cloud.github.com/assets/566742/2190716/48f66efe-9830-11e3-922d-788345be80da.png)