sync: log conformance errors if they happen

also send them via API to see them on admin
bump ruby version to 2.1.2 for travis
do not fatal with simple PKs

For conformance errors, some models' primary key will be a single value and JSON deserialization will fail. Return serialized primary key if deserialization fails
Enhance `NationalMeasurementUnitView`

- show national measurement unit only if available in map (see `NationalMeasurementUnit`)
- use parenthesis `(` instead of brackets `[`
upgrade to ruby 2.1.2
Merge pull request #197 from bitzesty/sync-conformance-errors

sync: log conformance errors if they happen
Merge pull request #200 from bitzesty/enhance-national-measurement-unit-view

Enhance `NationalMeasurementUnit` view
[Rails] update to version 3.2.19
Merge pull request #201 from bitzesty/rails-update-to-3-2-19

[Rails] update to version 3.2.19
Merge pull request #199 from bitzesty/ruby-2.1.2

upgrade to ruby 2.1.2
ME1 validation should not include export_refund_nomenclature_sid

Documentation states:
The combination of
measure type +
geographical area +
goods nomenclature item id +
additional code type +
additional code +
order number +
reduction indicator +
start date

must be unique.
Merge pull request #202 from alphagov/ME1

ME1 validation should not include export_refund_nomenclature_sid
Rollback entries for tariff-admin in descending order

As the list grows its better to view these in descending order
Clean up travis file and cache gems
Merge pull request #205 from alphagov/travis-update

Clean up travis file and cache gems
Merge pull request #204 from bitzesty/rollbacks-desc

Rollback entries for tariff-admin in descending order
Add some docs
Readme update

TARIC & CHIEF capitalisation, minor language tweaks
Update tariff_synchronizer comments
update docs of base_update