2893: Prevent symbol keys/values in serialized attributes.
2893: Add test for un-symbolizing existing db content.
2893: Add more tests for bogus serialized hash values.
2893: Add test cases. Stringify all serialized attrs coming from DB,
not just Hash. Rename has_any_symbols? to has_symbols?.
2893: Merge branch 'master' into 2893-no-symbols-in-db

Conflicts:
	services/api/test/fixtures/links.yml
2893: Merge branch '2893-no-symbols-in-db' closes #2893