Add an enabled option to be able to disable the controls

[vincentfretin]

We should add an enabled option on blink-controls to be able to disable it with
el.setAttribute('blink-controls', 'enabled', false)
See discussion in c-frame/aframe-extras#414

[vincentfretin]

I just wanted to mention it, because it was not in my linked issue and also I just figured it out myself reading again the code, Ada's experience is using a blink mixin to be able to easily remove blink-controls and add it again mainly because of this missing feature I guess:
https://github.com/AdaRoseCannon/aframe-xr-boilerplate/blob/19f42f0b0cefb64dba0a230131a57e8e16fe2cd4/index.html#L248-L255

[jure]

I'm definitely in favour of a way to enable/disable blink-controls! Is this something you could make a PR for?

[vincentfretin]

Of course this is something I can make a PR for, like other 10 PR I want to work on that are on my todo list. This one is not at the top though, there are others PR on HTMLMesh and aframe-cursor-teleport I need to do first.
If anyone want to work on it, please go ahead, I'll be happy to review it.