Add tests for the new Interval parsing.
Close #49
Merge branch 'enhancement-#49' into develop
Add DBHelper.
Update text XML file with correct UN_CODEs
Update tests to remove API Helper mock
Substitute APIHelper for DBHelper
Update requirements.txt

Remove 'requests' package, now unused because there is no need to
send requests to the API anymore.
Merge branch 'enhancement-#50' into develop