Respect relative URL for relation auto-completion
Merge pull request #2244 from opf/hotfix/17485_relation_autocomplete_broken_with_relative_url

17485 Relation auto-completion broken with relative URL
Merge branch 'release/4.0' into dev

Signed-off-by: Alex Coles <alex@alexbcoles.com>

Conflicts:
	frontend/app/helpers/path-helper.js
	frontend/app/work_packages/view_models/common-relations-handler.js