new option: "hotSpotFadeSpeed"

summary:
  * this value sets the duration (in milliseconds) of the fadeIn/fadeOut animation
  * previously, it was hard-coded to: 250 ms

methods it applies to:
  * showHotSpotBackgrounds
  * hideHotSpotBackgrounds

notes:
  * accepts an integer value
  * to not show any animation, set value to: 0