Fix persistence problem with plugin registration.

- Move the PluginManager creation to a service.
- Move plugin discovery to creation.
- Create static discovery and namespaces variables in the PluginManager.php library
- Refactor persistent namespace declarations
- Refactor redundant code to private function.
- Remove whitespace
- Remove enable setting from MailchimpPlugin. That is handled by the PluginManager.php
- Update Events.php to call the pluginManager service
- Correct typo in enabled setting for BasePlugin to accurately reflect the database naming.

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

app/Controllers/Plugins.php

@@ -12,8 +12,7 @@ class Plugins extends Secure_Controller
     public function __construct()
     {
         parent::__construct('plugins');
-        $this->pluginManager = new PluginManager();
-        $this->pluginManager->discoverPlugins();
+        $this->pluginManager = service('pluginManager');
     }
 
     public function getIndex(): string