Create new plugin `NLDS Gravity Forms Add-on`

[paulAcato]

Create new plugin NLDS Gravity Forms Add-on;

On activation:

• Check for required plugin: Gravity Forms, activate Gravity Forms if it's installed but not activated, disable the plugin when the required plugin is not installed;
• If it has Gravity Forms check for the version, if we support it or not, if not: Show an admin notification to update Gravity Forms;

Add a composer.json ;-)