Mouse Scroll overlay (MathewSachin#515)

Display Up/Down arrow when scrolling.

**New options added in Settings/Overlays/Mouse:**
- Display Scroll
- Scroll Circle Color
- Scroll Arrow Color

fixes MathewSachin#480 

#### Known Issues
- Horizontal scroll is displayed incorrectly as vertical scroll. The MouseKeyHook library doesn't tell whether the scroll was vertical or horizontal.
- Some touchpad scrolls may not be detected. This is an issue with how the touchpad drivers work. I can't really do much about that.