Jetty9 API Changes

These are the changes to the Jetty9 Webservice API that are being made to make this service consistent with the API of the web-routing service. 
Perhaps the same comment about about `:context-listeners` applies here as well?

Assuming those two can be simplified, there will be 5 occurrences of
```clj
(let [defaults  {:server-id :default}
      opts      (merge defaults options)
```
Seems like something to introduce a new function for ... or perhaps that's unnecessary if `get-server-context` is changed to interpret a `nil` `server-id` as `:default`.