Play sequence only while button is pressed

[Vafo]

In current implementation, program always iterates through all LEDs.
Change this logic.

Iterate only when a button is pressed.
If the button is pressed, released, and pressed again continue from the previous active LED.

Example for the sequence: RRGGGB

Button released => nothing
Button pressed for a 3 sec => RRG
Button released => nothing
Button pressed for a 2 sec => GG
Button released => nothing
Button pressed for a 5 sec => BRRGG

[Vafo]

Even though it is not really Discrete.
i.e. 2 consecutive presses != 2 cycles. 2 Presses can happen in span of 1 second resulting in 1 cycle.
Might consider implementing this feature