Settings API Primary Document refactor

Closes #2606

- Refactor settings api responses to { settings: [ ] } format
- Update all code using api.settings to handle new response format
- Update test stubs to return new format
- Update client site settings model to parse new format into one object of key/value pairs
- Refactor to include all setting values
- Remove unused settingsCollection method
- Update settingsCache to store all attributes
- Update settingsResult to send all attributes
- Remove unnecessary when() wraps
- Reject if editing a setting that doesn't exist
- Reject earlier if setting key is empty
- Update tests with new error messages
- Use setting.add instead of edit that was incorrectly adding
- Update importer to properly import activePlugins and installedPlugins
- Update expected setting result fields
- Fix a weird situation where hasOwnProperty didn't exist :shrug:
Merge pull request #2661 from jgable/settingsPrimaryDocument

Settings API Primary Document refactor