(TK-3) Add support for multiple servers

Add support for multiple servers to the jetty9 webservice. Previously, a user would define the webserver key in the configuration file as a map of configuration data, which would be used to configure a single Jetty9 server. This syntax is still valid. However, now the user can also define the webserver key as a nested map, where each key is the id of a server and each value is a map of configuration data (of the same form as before). With this information, the Jetty9 service will now initialize, start-up, and shutdown multiple servers if so specified by the user.
My main reasoning for not including a version that just goes to default is that these functions were just added last week, so I figured we wouldn't need to worry about compatibility with projects using the old versions of the functions from before the multi-server change. However, it definitely might be worth keeping default versions of those functions, especially for the sake of consistency, so I think I'll go ahead and add those back in.