Move GUI value init

[ThatOneRuffian]

On start-up this gui.* should be moved as it interferes with the resetting and initial start of the metronome - nil pointer, etc.

func (m *metronome) StartMetronome() {

	gui.TempgoStatData.MetronomeBeatsPerMeasure.Set(fmt.Sprint(MainMetronome.beatsPerMeasure))
	gui.TempgoStatData.MetronomeCurrentBPM.Set(fmt.Sprintf("%d BPM", MainMetronome.CurrentTempo))
	gui.TempgoStatData.MetronomeBeatInterval.Set(fmt.Sprintf(" %.0fms", 60_000.0/float32(MainMetronome.CurrentTempo)))