WIP es7 compliant contains

- [x] es7 polyfil for contains
- [ ] get review on the poly

--------------------------

- [ ] make enumerable stuff work correctly (ideally without lots of duplication)
- [ ] transition SHIM_ES5 to SHIM_ESNEXT

Also what if you pass more than 2 arguments `[1,2,3].contains(1, 1, 'oops');`