Make steps and loops more pythonic using decorators

[maartenuni]

This is perhaps an idea to make psylib get a more pythonic feel:

Create decorators for stepping stones and loops:

@Loop(0, 10, 1, Psy.LoopCondition.LESS)
def on_iteration():
    pass

stones = Psy.SteppingStones()

@stones.on_enter
def my_callback():
    stones.activate_next_by_name('blue')

@stone.on_leave
def stone_on_leave():
    pass

This is perhaps better done in Python helper scripts than from psylib itself.