Moves some search tests to spec
Adds spec
Fixes missing work package url
Adds changelog entry
adds translation for general 'not_a_valid_parent' error
uses correct error messages for nested set work package validations
Changelog

Conflicts:
	doc/CHANGELOG.md
Merge pull request #748 from opf/fix/work_package_parent_errors

Fix/work package parent errors
Merge pull request #747 from opf/fix/search_work_package_result_link_3303

[FIX] Search work package result link
Fixed parent attribute error message
Reverts 687db52 for projects controller test
Merge remote-tracking branch 'origin/dev' into feature/issue_autocomplete