[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/ArrayOfArrayOfNumberOnly.php

@@ -0,0 +1,15 @@
+<?php
+/**
+ * ArrayOfArrayOfNumberOnly
+ */
+namespace OpenAPIServer\Model;
+
+/**
+ * ArrayOfArrayOfNumberOnly
+ */
+class ArrayOfArrayOfNumberOnly {
+
+    /** @var float[][] $arrayArrayNumber */
+    private $arrayArrayNumber;
+
+}