[PHP] Support for customizing namespace and Composer fields

[who]

I've improved the configuration file support in the PHP codegen so that composer vendor name, composer project name, composer version, and namespace are all configurable.

Here's the new output of the config-help for php:

java -jar ./modules/swagger-codegen-cli/target/swagger-codegen-cli.jar config-help -l php

CONFIG OPTIONS
    modelPackage
        package for generated models

    apiPackage
        package for generated api classes

    invokerPackage
        The main namespace to use for all classes.

    packagePath
        The main package name for classes.

    srcBasePath
        The directory under packagePath to serve as source root.

    composerVendorName
        The vendor name used in the composer package name. The template uses {{composerVendorName}}/{{composerProjectName}} for the composer package name.

    composerProjectName
        The project name used in the composer package name. The template uses {{composerVendorName}}/{{composerProjectName}} for the composer package name.

    artifactVersion
        The composer package version used to generate the composer.json file.

[who]

Here is an example of what this PR allows, given the petstore 2.0 spec:

Given this config json...

{
    "invokerPackage": "Yay\\Pets",
    "modelPackage": "Yay\\Pets\\MyModelPackage",
    "apiPackage": "Yay\\Pets\\MyApiPackage",
    "packagePath": "GeneratedPetstore",
    "composerProjectName": "petstore-client",
    "composerVendorName": "yaypets",
    "artifactVersion": "1.2.3"
}

... this is the swagger-codegen output ...

java -jar ./modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate -l php -i http://petstore.swagger.io/v2/swagger.json -o output -c config.json
reading config from config.json
reading from http://petstore.swagger.io/v2/swagger.json
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/MyModelPackage/Order.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/MyModelPackage/Category.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/MyModelPackage/User.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/MyModelPackage/Tag.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/MyModelPackage/Pet.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/MyModelPackage/ApiResponse.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/MyApiPackage/UserApi.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/MyApiPackage/PetApi.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/MyApiPackage/StoreApi.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/Configuration.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/ApiClient.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/ApiException.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/lib/ObjectSerializer.php
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/composer.json
writing file /tmp/tmp.cxkWt5lE73/swagger-codegen/output/GeneratedPetstore/autoload.php

... and this is the file tree of generated output ...

GeneratedPetstore/
├── autoload.php
├── composer.json
└── lib
    ├── ApiClient.php
    ├── ApiException.php
    ├── Configuration.php
    ├── MyApiPackage
    │   ├── PetApi.php
    │   ├── StoreApi.php
    │   └── UserApi.php
    ├── MyModelPackage
    │   ├── ApiResponse.php
    │   ├── Category.php
    │   ├── Order.php
    │   ├── Pet.php
    │   ├── Tag.php
    │   └── User.php
    └── ObjectSerializer.php

... and this is the composer.json:

{
    "name": "yaypets/petstore-client",
    "version": "1.2.3",
    "description": "",
    "keywords": [
        "swagger",
        "php",
        "sdk",
        "api"
    ],
    "homepage": "http://swagger.io",
    "license": "Apache v2",
    "authors": [
        {
            "name": "Swagger and contributors",
            "homepage": "https://github.com/swagger-api/swagger-codegen"
        }
    ],
    "require": {
        "php": ">=5.3.3",
        "ext-curl": "*",
        "ext-json": "*",
        "ext-mbstring": "*"
    },
    "require-dev": {
        "phpunit/phpunit": "~4.0",
        "satooshi/php-coveralls": "~0.6.1",
        "squizlabs/php_codesniffer": "~2.0"
    },
    "autoload": {
        "psr-4": { "Yay\\Pets\\" : "lib/" }
    }
}

[who]

@wing328 let me know if you need me to elaborate on any of this.

[wing328]

@who thanks for the PR! I'll review and let you know if I've any questions.

[wing328]

Unit testing looks good:

SwaggerClient-php|develop_2.0 ⇒ ./vendor/bin/phpunit tests




PHPUnit 4.7.7 by Sebastian Bergmann and contributors.

............

Time: 8.86 seconds, Memory: 16.75Mb

OK (12 tests, 2576 assertions)

Tested with the config json provided and the result also looks good.