Implement fix: KeyboardHelper may damage site functionality

[fmiu-imperosoftware]

The KeyboardHelper may brake site functionality because it add/remove document keyboard event listeners using event handlers properties. If the parent site has already some event listeners added in the same manner they are removed by this code and the site functionality is damaged.

  GrabKeyInput (): any {
    if (this.KeyInputGrab) { return }
    document.onkeyup = this.handleKeyUp.bind(this)
    document.onkeydown = this.handleKeyDown.bind(this)
    document.onkeypress = this.handleKeys.bind(this)
    this.KeyInputGrab = true
  }
  UnGrabKeyInput (): any {
    if (!this.KeyInputGrab) { return }
    document.onkeyup = null
    document.onkeydown = null
    document.onkeypress = null
    this.KeyInputGrab = false
  }

Using addEventListener/removeEventListener would be better, to preserve any previous event handlers.

constructor () 
    this.handleKeyUp = this.handleKeyUp.bind(this)

GrabKeyInput
    document.addEventListener('keyup', this.handleKeyUp)

UnGrabKeyInput 
    document.removeEventListener('keyup', this.handleKeyUp)