Added deviceId parameter to the scene - it will set what camera to us…

[alfallouji]

…e based on its deviceId

What kind of change does this PR introduce?

This is a new feature - allows to define the deviceId to use for the camera.

** Can it be referenced to an Issue? If so what is the issue # ?**
Might be useful for this issue : #178

How can we test it?

You can use this feature by defining the deviceid as a parameter in the scene, like this :
<a-scene embedded arjs="detectionMode: mono_and_matrix; matrixCodeType: 3x3; sourceType: webcam; trackingMethod: best; debugUIEnabled: false; deviceId: 10d9f755ccab290ef5dbd4a1bb27cca11e61677ab0b4356f302e098ef6144813;" antialias="true">

In order to get the deviceId, you can use getUserMedia.

Summary

Does this PR introduce a breaking change?
It doesn't. The previous behaviour to select what camera to pick up is the default one. The deviceId parameter is optional.

Other information

[jeromeetienne]

looks good to me. anybody can test it ?

[mnutsch]

I tested this.
It did not seem to work in either the Chrome browser or the Edge browser.
I added a GET variable to the URL with the name "deviceId". I set the value to the deviceId of a camera connected to the computer.
AR.js still opened with the default camera.
Perhaps more instructions should be added on how to use this feature.

[alfallouji]

I just noticed that the code sample on how to test it got hidden (forgot to put it between code markdown) ! You need to provide the deviceId in the scene tag, like this :

<a-scene embedded arjs="detectionMode: mono_and_matrix; matrixCodeType: 3x3; sourceType: webcam; trackingMethod: best; debugUIEnabled: false; deviceId: 10d9f755ccab290ef5dbd4a1bb27cca11e61677ab0b4356f302e098ef6144813;" antialias="true">

[mnutsch]

I tested this with the added instructions and I confirmed that this change works as described.