Rm unused variable defined in global namespace

Tiny fix, detected accidentally by mocha.
Update RequireJS config for tests

[#43328491]

Support modules which use backbone.
Simplify validator, use jQuery.extend when possible
Move interactive validation to a separate method

[#43328491]
Test serialization of the interactive state

[#43328491]

This is first test, which uses our existing interactives, loads them,
serializes and finally compares. Another useful test would be to
modify interactive after initialization and later serialize (TODO).