(TK-10) Add get-registered-endpoints function with tests

I've added the get-registered-endpoints function to the service and have written some tests to go along with it. Whenever one of the service functions is called, a set in the state is updated with a map containing information on the endpoint and what created that endpoint. This set is then returned by the get-registered-endpoints function.
Couldn't this just be `(:state s)` based on  your previous line?

Alternately you could do:

```clj
(-> (service-context this)
    :jetty9-server
    :state)
```
or:
```clj
(get-in (service-context this) [:jetty9-server :state])
```