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.
> refactoring did indeed remove redundant code, see condensed refactoring below:
Why is this, and the following 4 lines, still here? Isn't it executed above, before the **if (needFirstDraw) {** line?