Couple changes and fixes...

- switched out the Host and Join buttons for one Play button
- when the player is in game and hits ESC they will be sent back to the
main menu
- fixed the annoying path finding bug... EnemyAI checks for the size of
pathFinder.nodes but sometimes those nodes haven't loaded yet which I
guess has to do with how Unity loads objects and which get loaded first.
Made a simple check to prevent the bug. Also in PathFinder I moved the
finding of the nodes into the update method to ensure that they do
eventually get added to the list because again sometimes PathFinder
loaded before all the nodes did.