addAll(property, amount, checkAlive, checkVisible)
 Adds the amount to the given property on all children in this group. Group.addAll('x', 10) will add 10 to the child.x value for each child. 
Parameters
Name Type Description property  string  The property to increment, for example 'body.velocity.x' or 'angle'. amount  number  The amount to increment the property by. If child.x = 10 then addAll('x', 40) would make child.x = 50. checkAlive  boolean  If true the property will only be changed if