Mailchimp PLugin

- Corrected grammar in PHPdocs
- PSR refactoring of local variables and code blocks
- Moved MailchimpPlugin.php to its own plugin folder
- Refactored out mailchimp code to the plugin
- Created customer_loaded event trigger

Signed-off-by: objec <objecttothis@gmail.com>

app/Libraries/Plugins/PluginInterface.php

@@ -14,10 +14,10 @@ interface PluginInterface
 
     /**
      * Register event listeners for this plugin.
-     * 
+     *
      * Use Events::on() to register callbacks for OSPOS events.
      * This method is called when the plugin is loaded and enabled.
-     * 
+     *
      * Example:
      *   Events::on('item_sale', [$this, 'onItemSale']);
      *   Events::on('item_change', [$this, 'onItemChange']);
@@ -26,7 +26,7 @@ interface PluginInterface
 
     /**
      * Install the plugin.
-     * 
+     *
      * Called when the plugin is first enabled. Use this to create database tables,
      * set default configuration values, and run any setup required.
      */
@@ -34,7 +34,7 @@ interface PluginInterface
 
     /**
      * Uninstall the plugin.
-     * 
+     *
      * Called when the plugin is being removed. Use this to remove database tables,
      * clean up configuration, etc.
      */
@@ -45,7 +45,7 @@ interface PluginInterface
     /**
      * Get the path to the plugin's configuration view file.
      * Returns null if the plugin has no configuration UI.
-     * 
+     *
      * Example: 'Plugins/mailchimp/config'
      */
     public function getConfigView(): ?string;
@@ -53,4 +53,4 @@ interface PluginInterface
     public function getSettings(): array;
 
     public function saveSettings(array $settings): bool;
-}
+}