SM-2314: Avoid IndexOutOfBoundsException in service operations (Closes #13)

If an invalid index is passed, throw a JAX-RS WebApplicationException
with HTTP code 404 ("Not found").

Signed-off-by: Gregor Zurowski <gregor@zurowski.org>
SM-2328: Downgrade to Karaf 2.3.4

(Cherry picked from the commit aebf7f2dfcfe689fbc5a8cb60aef8b3951e994ae)