Add CI checks that cookbook and reference examples work

[mikedotexe]

Currently we are not tracking whether changes made to this repo will break the demonstration snippets/examples in the examples directory.

We'll likely have to consider using contract helper for CI in order to create full-access keys for some of the tests that require sending native tokens, like the wrap-near.js example.

[chadoh]

Prerequisites:

• near/runner-js#39
• determine how we can keep these scripts simple & educational while also making it possible to test them in a controlled way.

[jberrytech]

Sprint planning comments: sandbox will unblock this.