Do not repeat ActiveSupport::Notification, shorter calls
Include 10 last SQL queries in synchronizer exception email
List queries in code tag

Easier to read in monospace
Meaningful exceptions when TARIC record is not found

Will say that record was not found instead of:
"undefined method `set' for nil:NilClass`" which is a consequence of
record not being found
Rework TariffSynchronizer update fetching

Synchronizer used to stop checking for updates for the day after it
found its first CHIEF/Taric match. After recent update process outage in
production we noticed that TARIC updates may appear twice at different
times of day. This update keeps continuously checking for TARIC and
CHIEF updates throughout the day.
Merge pull request #120 from alphagov/tariff-synchronizer-enhancements

Tariff synchronizer enhancements
https://www.pivotaltracker.com/story/show/59042540