Update jshintrc to conform to new style guide. Conform to onevar and unused in tests. Fixes #13755.

Conflicts:
	src/.jshintrc
	src/data.js
	test/unit/attributes.js
	test/unit/core.js
	test/unit/data.js
	test/unit/event.js
	test/unit/manipulation.js
	test/unit/queue.js
	test/unit/traversing.js
	test/unit/wrap.js