Fix Bugs

• fix getter and setter methods of SpeedometerBackColor for TubeSpeedometer.
• fix color doesn't change at runtime for TubeSpeedometer.
• fix color changed in RecyclerView at runtime #100 .
• fix center circle color for PointerSpeedometer #106 .
• New custom number of decimal for speedText and Ticks #108 .
  you can use:

// add 4 decimal places for speedText.
speedometer.setSpeedTextFormat(4);