WPForms GetResponse Addon 1.7.0

### IMPORTANT
- Support for PHP 5.6 has been discontinued. If you are running PHP 5.6, you MUST upgrade PHP before installing WPForms GetResponse 1.7.0. Failure to do that will disable WPForms GetResponse functionality.
- Support for WordPress 5.4 and below has been discontinued. If you are running any of those outdated versions, you MUST upgrade WordPress before installing WPForms GetResponse 1.7.0. Failure to do that will disable WPForms GetResponse functionality.

### Added
- Compatibility with WPForms 1.8.9.

### Changed
- The minimum WPForms version supported is 1.8.9.

### Fixed
- Create or Update action could lose subscriber tags and custom fields if a subscriber was already in the GetResponse list.

### Changed
- Minimum WPForms version supported is 1.8.3.

### Fixed
- The fatal error was thrown when users were trying to create a connection in the Form Builder with an expired API key.

### IMPORTANT
- Support for PHP 5.5 has been discontinued. If you are running PHP 5.5, you MUST upgrade PHP before installing the new WPForms GetResponse and WPForms 1.7.3 (that the addon is relying on). Failure to do that will disable the WPForms GetResponse plugin.
- Support for WordPress 5.1 has been discontinued. If you are running WordPress 5.1, you MUST upgrade WordPress before installing the new WPForms GetResponse. Failure to do that will disable the new WPForms GetResponse functionality.

### Added
- Compatibility with WPForms 1.6.8 and the updated Form Builder.

### Changed
- Minimum WPForms version supported is 1.7.3.

### Fixed
- Compatibility with WordPress Multisite installations.
- Properly handle the situation when trying to change the template for the same form multiple times.
- Send to GetResponse form submission data even when the "Entry storage" option is disabled in the Form Builder.