some changes to playlab script

Start of some changes to playlab script. Still a few more coming.

Also included a couple of code changes
- Allow you to override goal images (to use fireball instead of flag)
- Allow you to specify the avatarList in the level definition (otherwise you're restricted to using the avatars in the default list in the order they are there).
Er, rather, that every tick # exists, was probably a silly question anyway :)