Update database seeds with the dummyapiuser for development

The gds-sso gem mock MockBearerToken strategy if it cannot find a user
will call dummy_api_user.save! Sequel defaults to raising exceptions
when save fails and doesn't have a save! method, we could alias it
but adding the dummy user resolves the issue.

https://github.com/alphagov/gds-sso/blob/master/lib/gds-sso/bearer_token.rb#L56
Remove FACTER_govuk_platform from code.

In all of our current multi-vm environments:
    `ENV['FACTER_govuk_platform']=='production'`
Which means it's exactly the same as Rails.env

This commit removes it from the code.
Merge pull request #181 from alphagov/remove-govuk_platform

Remove FACTER_govuk_platform
Measurement unit abbreviation enhances

Include `national_measurement_units` as part of `formatted_base`
Include `national_measurement_units` as part of `base`

`national_measurement_units` won't be serialised anymore to frontend
Merge pull request #196 from bitzesty/measurement-unit-abbreviation-enhances

Measurement unit abbreviation enhances
show missing abbreviation tags for measurement abbreviations
Merge pull request #198 from bitzesty/measurement-abbreviations-enhances

show missing abbreviation tags for `ps/t` abbreviation