Offer the possibility to override internal formatter objects from plugins

tests/units/ServiceProvider/ClassProviderTest.php

@@ -0,0 +1,21 @@
+<?php
+
+use Kanboard\ServiceProvider\ClassProvider;
+use Pimple\Container;
+
+require_once __DIR__.'/../Base.php';
+
+class ModelProviderTest extends Base
+{
+    public function testServiceInstance()
+    {
+        $container = new Container();
+        $serviceProvider = new ClassProvider($container);
+        $serviceProvider->register($container);
+
+        $instance1 = $container['userModel'];
+        $instance2 = $container['userModel'];
+
+        $this->assertSame($instance1, $instance2);
+    }
+}