Add two finger rotation to control rotation

[DIYer22]

It's hard to control rotation in touchable screen, so may add two finger rotation to control rotation?

[syt123450]

@DIYer22 Thanks for your suggestion, now TensorSpace mainly use a three.js plugin TrackballControl to control events, it may has some limitation in touch device. It is possible to registered new events for TensorSpace, which are not included in TrackballControl.

Now, user can use two fingers to zoom in or out, translate model in the scene in the touch device, these touch events are provided by TrackballControl. Honestly, I don't have experience adding android's two finger rotation to website, and I am afraid I will break the TrackballControl's functionality QAQ.

If you have any idea how to implement this amazing functionality, feel free to propose it to us or send us a PR ~