Support default-server option in webrouter

Modify the webrouting service so that it defaults to using the
default server set in the webserver service configuration rather
than a server with id :default.
Test default server requirement for webrouter

Add a test to the webrouting service that ensures that a default
server is required if any endpoints are not configured with
servers
Merge pull request #55 from fpringvaldsen/webrouting-fix

Use webserver's default server in the webrouter