[Slim] Improve codebase decouple (#438)

* [Slim] Decouple Api files into separated PHP Classes

This enhancement required for modular testing and code coverage generating.

* [Slim] Define all app routes in SlimRouter PHP Class. Generate new samples

samples/server/petstore/php-slim/lib/Model/EnumArrays.php

@@ -0,0 +1,18 @@
+<?php
+/**
+ * EnumArrays
+ */
+namespace OpenAPIServer\Model;
+
+/**
+ * EnumArrays
+ */
+class EnumArrays {
+
+    /** @var string $justSymbol */
+    private $justSymbol;
+
+    /** @var string[] $arrayEnum */
+    private $arrayEnum;
+
+}