Gravity Perks - Terms Of Service 1.4.7

Fixed an issue where multiple Terms of Service checkboxes would not function correctly when the "Require Full Scroll" option was enabled.

Fixed issue where the checkbox for Terms of Service could be switched to disabled after a validation failure which could then cause form submission to fail if there is conditional logic that depends on the Terms of Service field.
Updated require call to use plugin_dir_path().

Updated Perk to use GP_Plugin class provided by Gravity Perks 2.0.