[Slim] Upgrade API server integration tests to use Fake Petstore spec (#354)

* [Slim] Shell script points to petstore-with-fake-endpoints-models-for-testing.yaml. Slim init and new models has been generated.

* [Slim] Bugfix. Special value */* in opperation produces escaped to avoid PHP syntax errors.

* [Slim] Add own private static final LOGGER

* [Slim] Bugfix. toModelName method copied from PHPClient codegen which handles Fake Petstore spec much better.

* [Slim] Sort operations in supporting files data to avoid shadowing static routes.

* [Slim] Mustache index.php update. Params parsing enhanced.

* [Slim] Tiny cleanup. Unnecessary empty space removed.

* [Slim] Security fix. toOperationId method copied from PhpClientCodegen.

* [Slim] Bugfix. formData params parsing restored.

* [Slim] Proper .gitignore added to PhpSlimServerCodegen. Vendor folder with all dependencies removed to keep repo more clean.

* [Slim] Slim dependency update to 3.10.0. Few test fake endpoints fixed by this upgrade.

samples/server/petstore/php-slim/lib/Models/ArrayOfArrayOfNumberOnly.php

@@ -0,0 +1,13 @@
+<?php
+/*
+ * ArrayOfArrayOfNumberOnly
+ */
+namespace \Models;
+
+/*
+ * ArrayOfArrayOfNumberOnly
+ */
+class ArrayOfArrayOfNumberOnly {
+    /* @var Number[][] $arrayArrayNumber  */
+    private $arrayArrayNumber;
+}