(TK-68) Allow the user to specify static content to be added during initialization

This PR adds an optional key to server configurations, `:static-content`. This key contains a list of maps, with each map representing static content that will be added to the server when it is initialized.
I think we should use a different example here.  Perhaps serving an image file from an `assets` directory, or something more conventional.  Serving up a logback config file is probably not how people are going to use this.  :)