Add support for Third Party Settings

Problem

YAML form needs to support third party integration which immediately includes the Honeypot module. (https://www.drupal.org/project/honeypot)

Solution

Use Drupal's ThirdPartySettingsInterface and build extendable Third Party (Settings) forms.

User interface changes

Third Party tabs will be added to the YAML form admin settings and YAML form config entity settings.

Tasks

• Setup Third Party admin settings tab. (admin/structure/yamlform/settings/third-party )
• Setup Third Party YAML form settings tab (admin/structure/yamlform/manage/{yamlform}/third-party)
• Build yamlform_test_third_party.module which just enables a warning on a form.
• Setup yamlform_third_party_load_includes(). See \Drupal\Core\Extension\ModuleHandler::loadAllIncludes()
• Setup config schema for third party settings. See .third_party.[%key]
• Implement yamlform_test_third_party hooks.
• Delete third party settings when module is uninstalled
• Write tests
• Update API documentation.
• Update README.md

Notes

• YAML form config entity already implements ThirdPartySettingsInterface
• YAML form admin settings does not have a concept of third party settings.
• YAML form module will support implementing third party setting on a contrib modules behalf. Set up yamlform/third_party_settings/yamlform.third_party_settings.{module_name}.inc

Development Notes

• Branch Name: 2707857-yaml-form-third-party-settings
• Patch Name: yaml-form-third-party-settings-2707857-XX.patch
• Commit message: Issue #2707857: Add support for Third Party Settings.

References

• http://www.webomelette.com/drupal-8-custom-data-configuration-entities-u...
• http://www.sitepoint.com/drupal-8-third-party-settings-and-pseudo-fields/