led_effects: Clarify blocking nature of countdown
* The 'int' return signature and the comment 'Returns the number of remaining leds' sounds like the function would return its current countdown state. However, it only returns the number of remaining leds after the button was released. Thus change the type to 'bool' and return 'true' after a successful countdown * Do not use 1 as return value for night mode, because it is ambigous. Return 'false' instead.