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

Here are some [other implementations and benches](http://jsperf.com/contains-vs-index-of/7).