Lots of testing, both on expected and insane values.

Change-Id: Id4b2511897347ce7985dcb44837a1a33cd5e9169
Signed-off-by: Filip Wieland <filiplamparski@gmail.com>
Minor changes to the test program

Change-Id: Id65f4d2a4432174b8210a4de3ae68b408c9eb29c
Signed-off-by: Filip Wieland <filiplamparski@gmail.com>
Refactored delivery.Dataset to use Maps because ONS is stupid.

A lot of calls now throw ValueNotAvailable instead of returning null,
because that's easier to test, and I want client code to be prepared for
the N/A cells (which pop up in weird places actually, see top line).

Change-Id: I63c71fcbc6b37b724ca159c985dee2a27508b8af
Signed-off-by: Filip Wieland <filiplamparski@gmail.com>