Allow plugins loading from another location

app/Core/Plugin/Loader.php

@@ -2,6 +2,7 @@
 
 namespace Kanboard\Core\Plugin;
 
+use Composer\Autoload\ClassLoader;
 use DirectoryIterator;
 use PDOException;
 use LogicException;
@@ -39,6 +40,10 @@ class Loader extends \Kanboard\Core\Base
     public function scan()
     {
         if (file_exists(PLUGINS_DIR)) {
+            $loader = new ClassLoader();
+            $loader->addPsr4('Kanboard\Plugin\\', PLUGINS_DIR);
+            $loader->register();
+
             $dir = new DirectoryIterator(PLUGINS_DIR);
 
             foreach ($dir as $fileinfo) {
@@ -69,7 +74,6 @@ class Loader extends \Kanboard\Core\Base
         $instance = new $class($this->container);
 
         Tool::buildDic($this->container, $instance->getClasses());
-
         Tool::buildDICHelpers($this->container, $instance->getHelpers());
 
         $instance->initialize();

composer.json

@@ -41,7 +41,6 @@
     "autoload" : {
         "classmap" : ["app/"],
         "psr-4" : {
-            "Kanboard\\Plugin\\": "plugins/",
             "Kanboard\\" : "app/"
         },
         "files" : [