Feature/jkarni/jsinput

DO NOT USE.
Non-stable version of jsinput with no tests! Putting in a PR already since it'll let us finish studio-izing 700x and removing the 700x-specific inputtypes from edx-platform, but if this input type is used in places I'm not aware of, I won't be able to ensure soon-to-be changes don't break content.

Reviewers/interested parties: @johnhess @shnayder @Lyla-Fischer @jmclaus