Add user's name to play screen
Creates new enemies when changing screen?
Only add global variable if appropriate - if user already signed in
If player has no existing mapId, placed in a random new screen
Fix world creation linking up maps bug by promisifying mongoose
Update users - places new player on random already existing screen rather than hard coding
No longer hard codes player's starting position
Check user name uniqueness on creation
Clean up routes a bit
Clean up build world slightly