Hook into Gravity Forms

[cliffordp]

References:

• http://gravitywiz.com/documentation/gp-terms-of-service/
• if not identical, but with the code: http://wpsmith.net/2011/plugins/how-to-create-a-custom-form-field-in-gravity-forms-with-a-terms-of-service-form-field-example/
• https://code.hyperspatial.com/all-code/wordpress-code/terms-of-service-custom-field-for-gravity-forms/