Groupd options for tags of type
Extract tag helper methods into separate helper
Include top-level tags in tag lists

There are use cases where things may need to be tagged with a top-level
tag in a tag type. To make this play nice within a multi-select field
and optgroups, this inserts the parent tag at the start of the optgroup.

Cherry pick Conflicts:

	test/integration/artefacts_edit_test.rb

I've not included the oil tags test, not needed by ODI.
Correctly handle nil values for tag array fields

There's a bug in Rails where parameters that are an empty array get
changed to be nil before being passed to the controller. This breaks
requests passing in an empty array of tags as the nil gets passed down
into the set_tags_of_type Taggable method, causing an exception in
Mongo.

This fixes the behaviour so that a nil value for a field matching the
tag types will get replaced with an empty array. This only applies to
fields which have a key present in the params hash, to make sure we
don't overwrite tags of every type.
Skipping for now

This test is specific to industry sector tags which ODI does not use.
I'm leaving it in as I think I'll need it in a few commits time and I can alter
it to be ODI specific.
UX improvement in gds-sso for remote logout

http://git.io/llA6Qw
govuk_content_models needed to be updated
to get this version of gds-sso through

Conflicts:

	Gemfile
	Gemfile.lock
Update README.md to reflect changes to auth
Add airbrake so we can send exceptions to errbit
Drop the legacy tags field from artefacts

Some artefacts contain a field called "tags", containing a string of
comma-separated keywords. This field has been long deprecated, and it
should be dropped.

This does not affect how tags are stored for artefacts, as the tag_ids
array is in use for this.
ApiUsers are Users, so this wasn't working

since api users started being a User using
bearer tokens this code was not of any use
anyways, so removing it.
Merge pull request #79 from theodi/gds_upgrade_tags_and_things

Gds upgrade tags and things