Add external links to artefact

So editors can add related external URLs to artefacts.
remove ordering by creation date
remove trailing whitespace
Merge pull request #80 from alphagov/related_external_links

Related external links
Make sure the URL is valid in artefact external links
Merge remote-tracking branch 'origin/related_external_links'
add nested attributes call
Merge remote-tracking branch 'origin/related_external_links'
Bump to 5.5
Add Travis config.
Fix missing `require` for simple smart answers.
Merge pull request #83 from alphagov/fix-missing-require

Fix missing `require` for simple smart answers.
Bump version to 5.5.1.
Merge remote branch 'origin/master' into simple-smart-answer-node

Conflicts:
	app/models/simple_smart_answer_edition.rb