Plugin architecture to support user add-ons

[billz]

Resolves #1692

[assachs]

I think "return false" is missing in PluginManager.handlePageAction

TypeError: RaspAP\Plugins\PluginManager::handlePageAction(): Return value must be of type bool, none returned
 at RaspAP.Plugins.PluginManager.handlePageAction(PluginManager.php:89)
 at require_once(page_actions.php:10)
 at (main)(index.php:116)

[assachs]

Also two Problems with sidebar:

Adblock is shown, but it's disabled:

$this->addItem(_('Ad Blocking'), 'far fa-hand-paper', 'adblock_conf', 40,
    fn() => defined('RASPI_ADBLOCK_ENABLED') && **RASPI_HOTSPOT_ENABLED** && !$_SESSION["bridgedEnabled"]
);

RestAPI:

$this->addItem(_('RestAPI'), 'fas fa-puzzle-piece', 'restapi_conf', 120,
    fn() => defined('**RASPI_VNSTAT_ENABLED'**) && **RASPI_VNSTAT_ENABLED**
);

[billz]

I think "return false" is missing in PluginManager.handlePageAction

In testing, the PluginManager did not handle multiple plugin instances. So this is still in active development.

Will look into the sidebar issues, thanks.

[billz]

@assachs these issues have been resolved. your testing is appreciated!

[assachs]

I migrated my plugin to the new plugin architecture. Everything worked very well. Thank you for implementing it.