Support 360 stereo images / videos and cubemap images for field type position

[weddingdj]

Support 360 stereo images / videos as well as cubemaps for field type position.

How do we know that it is a a stereo image, stereo video or image cubemap? - We could add a checkbox in the asset library to mark image or video as stereo or image as cubemap. So the field type position would know how to load the media (mono or stereo or cubemap).

[poVoq]

Or supply a overunder checkbox and implement this: https://github.com/bryik/overunder-aframe