Sweep and Clear 1.2

After more play-tests, I've updated Sweep and Clear:

1. I've simplified the alien placement and behaviour to make aliens more common and more aggressive.
2. I've changed the map so that the doors don't split the map into two halves, which made the game easier.
3. I've remove the choice of traits. Now there are four traits, not six. I took out what I think are the worst two, so now there's no choice and you can jump into the game quicker.

I still haven't added more missions. Once I'm happy with the mechanics that'll be the next step.