(TK-71/74) Improve Webrouting error messages

Improve error messages in the Webrouting service when
a specified service or endpoint does not appear in the
webrouting configuration and when the :web-router-service
section of the TK configuration is absent.
(TK-71/74) Change to IllegalArgumentException

Change the IllegalStateException thrown in the init function
of the webrouting service to an IllegalArgumentException.
Merge pull request #78 from fpringvaldsen/TK-71/74

(TK-71/74) Improve Webrouting error messages