add World::findPlayer for lookups as well as implement removeplayer

turn it into a list, much better than a vector for here. when the player
disconnects, every client will be told so, given a packet containing
playerID, they look that up, tell their own World to find that, remove
that, and then they do "something" with it (maybe), and delete it.
fix regression in player name sending. after the client's been verified

we send a packet to every client (including the one who just got
validated), and tell them there's a new player, the information like id
and name, position, camera, etc.
disconnect on SDL_QUIT
add client side player input direction
fix random num generator for player name, wasn't seeding it

but lets use C++11 mersenne twister randomness