Bind store methods before init() method executes.

Fixes #167.

I needed to update one unrelated test because the methods are bound before `this.listenToMany` runs. The alternative was moving the listenables handling earlier in the `Store()` constructor, but I was concerned that would break `init` methods that mutate `this.listenables`. As a note, `PublisherMethods.listen` is now getting passed bound store methods, so the callback binding it does is redundant for this case.