xeogl: obj pinch-zoom controls not responsive

[easyw]

Orbit works fine on touch screens,
zooming only ever zooms in and out of the actual webpage, making the image very pixelated;
panning doesn't work either.

Smartphone:

• OS: Android
• Browser: Firefox, Samsung stock

Note that Google Chrome on Android works fine instead.

Page to test:
http://xeogl.org/examples/importing_obj_parsing.html

I also noticed that this issue is also present i.e. if I load a gltf example
http://xeogl.org/examples/importing_gltf_BananaTree.html