[nipple-controls] rotation joystick only and move forward

[Vincent Fretin]

On this game https://animals.bio it uses a single virtual joystick that is actually the rotation virtual joystick (see #425) and it just moves forward when you touch the screen. I added some options to nipple-controls to disable one joystick or the other, see usage https://github.com/c-frame/aframe-extras/tree/master/src/controls#usage
and schema

aframe-extras/src/controls/nipple-controls.js

Lines 7 to 14 in d85de74

 mode: { default: "dynamic", oneOf: ["static", "semi", "dynamic"] }, 
 rotationSensitivity: { default: 1.0 }, 
 moveJoystickEnabled: { default: true }, 
 lookJoystickEnabled: { default: true }, 
 sideMargin: { default: "30px" }, 
 bottomMargin: { default: "70px" }, 
 moveJoystickPosition: { default: "left", oneOf: ["left", "right"] }, 
 lookJoystickPosition: { default: "right", oneOf: ["left", "right"] }, 

so enabling only rotation is nipple-controls="moveJoystickPosition: false"
but an option is missing to also move forward like moveForwardOnTouch:true (false by default)