Fixes for swift4 language (#6116)

* Fix build error in Xcode 9 beta 3, as .compact is no longer defined

* Add test schema for Swift 4 and associated script and config files

* Add test app for swift4Test.json schema

* Make integer, Integer, int, and Int32 types map to Swift Int type instead of Int32 type

* Add CodingKeys to model template, which allows us to serialize/deserialize variable names that are different than property names

* Make updates to Swift 4 test schema

* Fixes for unit test app for swift4Test.json Swift 4 test schema

samples/client/test/swift4/default/TestClientApp/Pods/Local Podspecs/TestClient.podspec.json

@@ -0,0 +1,22 @@
+{
+  "name": "TestClient",
+  "platforms": {
+    "ios": "9.0",
+    "osx": "10.11"
+  },
+  "version": "0.0.1",
+  "source": {
+    "git": "git@github.com:swagger-api/swagger-mustache.git",
+    "tag": "v1.0.0"
+  },
+  "authors": "",
+  "license": "Proprietary",
+  "homepage": "https://github.com/swagger-api/swagger-codegen",
+  "summary": "TestClient",
+  "source_files": "TestClient/Classes/Swaggers/**/*.swift",
+  "dependencies": {
+    "Alamofire": [
+      "~> 4.5"
+    ]
+  }
+}