Improve customizability of joystick view

[ramuno4]

Added the ability to pass in your own CircleView widgets to the JoystickView constructor, and choose a custom Icon to show around the joystick, allowing more visual flexibility.

The input CircleViews are forced to be of innerCircleSize so that the calculations cannot be affected The input icon only accepts IconData, so size cannot be directly controlled by the user

This would address issues 31, 27, 23