Code refactorings for MicroViewSlider

Replaced if/else blocks with switch, not sure if the originals where so because they could have been faster. Submitting for consideration anyways.

Simplified MicroViewSlider::draw() to remove redundant code.
Not sure I understand the question. This following block executed in both the if and else branch:

if (style==0 || style==1){		//Horizontal
		tickPosition = ((float)(uint16_t)(prevValue-getMinValue())/(float)(uint16_t)(getMaxValue()-getMinValue()))*totalTicks;
		uView.lineH(offsetX+tickPosition,offsetY, 3, WHITE, XOR);
		uView.pixel(offsetX+1+tickPosition,offsetY+1, WHITE, XOR);
	}
	else {					//Vertical
		tickPosition = ((float)(uint16_t)(getMaxValue()-prevValue)/(float)(uint16_t)(getMaxValue()-getMinValue()))*totalTicks;
		uView.lineV(offsetX+7, offsetY+tickPosition, 3, WHITE, XOR);
		uView.pixel(offsetX+6, offsetY+1+tickPosition, WHITE, XOR);
	}