Margrit/fix disco level

[maccxs]

This is based on #90, so merge #90 first.

• The npcs are placed randomly on the dancefloor not at the same position
• At the beginning three have the virus
• Adjusted the infection spread for this scenario (a little faster)
• The level can only be won if also the player has not been infected.

[holke]

Performance increased significantly, great. The level got easier, since the spreads is now slower. Was this indetended? I thought you liked the difficulty? If so, i will merge this.

For later: In my opinion, if the level is lost when the player returns infected (which is a good change), then the level could also end as soon as the player gets infected. Otherwise you get infected, fight another minute or so to get Jeff out, only to get the message then that you lost...a bit frustrating. Even more so if you know that you have lost now, but still have to walk to the exit to make the level end.

[maccxs]

Hi, I wanted the spread to be difficult but it's hard to get it done right. Please merge. This is only a small adjustment that we can try to set just right at a later point. The thing with the ending is also a good idea. I had that in mind at first, but it got lost in the end.