Allow setting vector lengths independent of amplitude

[eimrek]

weas related. @superstar54

Currently vector lengths are scaled by the factor input, and to get amplitude-independent vector lengths, i need to divide the factor by the amplitude, like so:

weas.avr.fromPhononMode({
      ...
      amplitude: amplitude * 5,
      factor: vectorLength / (amplitude * 5),
      ...
    });

This works, apart from the case where i want to set amplitude to 0, and still show oscillating vectors. Could the vectors and amplitude be completely independently specified? basically like

weas.avr.fromPhononMode({
      ...
      amplitude: amplitude * 5,
      vectorLength: vectorLength,
      ...
    });

[eimrek]

Note that i can currently bypass this by setting the minimum amplitude value to something very small but non-zero.