Added JSInput template to Studio. [BLD-523]
Using JSChannel lets JSInput bypass SOP. Studio template grades and saves state correctly with WebGLDemo situated on another domain.
Removed warning messages. A bit of code cleanup.
Added sop attribute to JSInput. Only if it's set to false, as in JSInput's template, will JSChannel be used to bypass it. In all other cases (attribute not present or set to something else), SOP is enforced. Compatibility with jsVGL is therefore maintained.
Put JSChannel in its own file. And instead of one, use two script placeholders to load it and JSInput.