TNT Fixes

TNT Fixes:
- TNT explodes other TNT blocks around it.
- TNT sends explosion packet to client.

I would've liked to add the Primed TNT entity but I notice you don't have an Entity class yet.

*Edit 1:* 
Didn't realize that github automatically adds any new commits that I make to the pull request. Anyway, I've added a very simple entity class now. I'll modify TNT to use it later.