More control over formation changes.

Allow to use :average1 .. :average6 and :fast1 .. :fast3 to allow more control over what player moves to a newer position.
The old way a single change in movement would cause a lot of movement and often leave the team vulnerable.

NOTE: This change is backward compatible. i.e.: the old way of specifying formations will still work.
I implemented backwards compatibility because I didn't want to rewrite previous coaches available on rubygoal.com and I wanted to train my new strategy against them.
But it's ok if you don't want to keep it.