Multiple levels

There was only support for one level on the server, so I had to refactor it. Basically I had to associate the players with levels. I also added storing and loading the levels from MongoDB. Everything seemed to go smoothly.

To see if multiple levels really work properly, there must be portals between the levels. I got one problem here, but it was a silly bug where I had = instead of ==. Next I added spawn points for levels. If there is no spawn point, the player will spawn at the same point it was in the previous level. The game runs surprisingly solidly considering how sloppily I have coded it. Next I'll add a dialog to select tools for level editing.