add a test runtime

[dvc94ch]

should be useful to test things like #103 or #91

should have a plain, map, double map store item and some transactions to deterministically modify them. we should also have a transaction that always returns an error and one that always returns an event.

[dvc94ch]

Using node-template for testing for now in #91 . It turns out that the same code that is needed for setting up a light client can be used for running tests locally.