fixes rounding issue in automatablemodel

[BaraMGB]

fixes #3075 (comment), #3661, #3659

[PhysSong]

Tested. It works well.

[Umcaruje]

Can you adress @zapashcanon's comment from here too: #3075 (comment)

Tested it out, works like a charm

[BaraMGB]

@Umcaruje yes, I noticed it. I'll change that line. 👍

[zonkmachine]

I've tested the last commit and it clears up the earlier stickyness. The code looks much better.

[redianthus]

All this code:

		if( qAbs( value ) >= step )
		{
			float roundedValue = qRound( ( oldValue - value ) / step ) * step;
			model()->setValue( roundedValue );
			m_leftOver = 0.0f;
		}
		else
		{
			m_leftOver = value;
		}

is duplicated, maybe something like:

	float consideredValue = value; // linear code

	if( model()->isScaleLogarithmic() ) // logarithmic code
	{
		const float pos = model()->minValue() < 0
			? oldValue / qMax( qAbs( model()->maxValue() ), qAbs( model()->minValue() ) )
			: ( oldValue - model()->minValue() ) / model()->range();
		const float ratio = 0.1f + qAbs( pos ) * 15.f;
		consideredValue = value * ratio;
	}

	if( qAbs( consideredValue ) >= step )
	{
		float roundedValue = qRound( ( oldValue - value ) / step ) * step;
		model()->setValue( roundedValue );
		m_leftOver = 0.0f;
	}
	else
	{
		m_leftOver = value;
	}

[tresf]

Cherry-picked to master via 902493b. Please target non-essential code cleanup at the master branch, once this fix is merged in.