Add international coverage data (http://www.royalmail.com/sites/default/files/RoyalMail_International_TrackedCoverage_Jan2014.pdf) and helper methods
Add logic to ensure that certain countries are excluded from signed, tracked+signed and tracked
Update tests to still work with the updated allowed countries.

We shouldn't be able to get international signed to France. So update to
Fiji where we can.
Add some tests to ensure the March 2014 limitations on signed, tracked and tracked+signed are honoured